Answer:
Part 1)
![IJ=2.3\ units](https://img.qammunity.org/2019/formulas/mathematics/middle-school/uo7few65qyoetfw9wtfg0cqragcijlg9xh.png)
Part 2)
![HJ=12\ units](https://img.qammunity.org/2019/formulas/mathematics/middle-school/9ac9qmmn0r6pfsu6u0fhu1p4ipvx95scu8.png)
Part 3)
![HJ=0.75\ units](https://img.qammunity.org/2019/formulas/mathematics/middle-school/km1f0qdybwnqzerk3ktpmoseadeju4mmi8.png)
Part 4)
![IH=4.7\ units](https://img.qammunity.org/2019/formulas/mathematics/middle-school/w5nuu0s4j3pf4qi6lpqp3hw9umz88evf2c.png)
Explanation:
Part 1) HI = 3.9 and HJ = 6.2. Find IJ
we have that
I is between H and J
![HJ=HI+IJ](https://img.qammunity.org/2019/formulas/mathematics/middle-school/qtyss0aixrlld3v3uqhwkli8oo3uozk4ji.png)
substitute the given values and solve for IJ
![6.2=3.9+IJ](https://img.qammunity.org/2019/formulas/mathematics/middle-school/dpa89i5fyggiv5mfnhvflru5mp63cg3t43.png)
subtract 3.9 both sides
![6.2-3.9=IJ](https://img.qammunity.org/2019/formulas/mathematics/middle-school/1js574s3xykaxil28ibjzp40r1vscrlwjp.png)
![2.3=IJ](https://img.qammunity.org/2019/formulas/mathematics/middle-school/j8myim7aiagrmaqg3g18p7cnakego74y90.png)
Rewrite
![IJ=2.3\ units](https://img.qammunity.org/2019/formulas/mathematics/middle-school/uo7few65qyoetfw9wtfg0cqragcijlg9xh.png)
Part 2) JI = 25 and HI = 13. Find HJ
we have that
H is between I and J
![IJ=IH+HJ](https://img.qammunity.org/2019/formulas/mathematics/middle-school/1pxhjhlejrqh5vbua2rhhs6rss0y3wjn7w.png)
remember that
IH=HI and IJ=JI
substitute the given values and solve for HJ
![25=13+HJ](https://img.qammunity.org/2019/formulas/mathematics/middle-school/ipy3ts59cxxq5d3lhurazyfu0ed3g42e4e.png)
subtract 13 both sides
![25-13=HJ](https://img.qammunity.org/2019/formulas/mathematics/middle-school/98lb8ycxtfwnhsw6ufy2us3bxbshhnf39n.png)
![12=HJ](https://img.qammunity.org/2019/formulas/mathematics/middle-school/s86hr0xe907i6s3s6htes47p6jbmfi00bq.png)
Rewrite
![HJ=12\ units](https://img.qammunity.org/2019/formulas/mathematics/middle-school/9ac9qmmn0r6pfsu6u0fhu1p4ipvx95scu8.png)
Part 3) H is the midpoint of IJ and IH = 0.75. Find HJ
we have that
H is between I and J and H is the midpoint of IJ
so
![IJ=IH+HJ](https://img.qammunity.org/2019/formulas/mathematics/middle-school/1pxhjhlejrqh5vbua2rhhs6rss0y3wjn7w.png)
----> because H is the midpoint
we have
![IH=0.75\ units](https://img.qammunity.org/2019/formulas/mathematics/middle-school/zm4oi1mab29ow5o1wb7nmoglj4otindzd2.png)
therefore
![HJ=0.75\ units](https://img.qammunity.org/2019/formulas/mathematics/middle-school/km1f0qdybwnqzerk3ktpmoseadeju4mmi8.png)
Part 4) H is the midpoint of IJ and IJ = 9.4. Find IH
we have that
H is between I and J and H is the midpoint of IJ
so
-----> equation A
----> equation B
substitute equation B in equation A
![IJ=2(IH)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/1xwyddgatuwc52kn18276fgsyen53ma7fz.png)
substitute the given value and solve for IH
![9.4=2(IH)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/2bk6mml5tsqw2webmuk7s8liq2icdf4iz8.png)
Divide by 2 both sides
![IH=4.7\ units](https://img.qammunity.org/2019/formulas/mathematics/middle-school/w5nuu0s4j3pf4qi6lpqp3hw9umz88evf2c.png)