Answer:
![QP=20\ units](https://img.qammunity.org/2021/formulas/mathematics/middle-school/yxub5o5zfz16fg04tv4gkpojp14tsijh73.png)
Explanation:
The picture of the question in the attached figure
Let
O ---> the center of the circle
we have that
Line segment QP is tangent to the circle
That means
OQ (radius) is perpendicular to segment QP
OQP is a right triangle
Applying Pythagorean Theorem
![OP^2=OQ^2+QP^2](https://img.qammunity.org/2021/formulas/mathematics/middle-school/qor8feoufoap17b54at6rqs67t9zp1w9uo.png)
we have
The radius is equal to
----> the radius is half the diameter
![OP=r+NP=12+11.5=23.5\ units](https://img.qammunity.org/2021/formulas/mathematics/middle-school/anf8y03fx6mj1sbkv0rvtx6ieb7j3ps36p.png)
![OQ=r=12\ units](https://img.qammunity.org/2021/formulas/mathematics/middle-school/t1g1cgiwnmc7430vxqil6rvlv3uslgb72k.png)
substitute
![23.5^2=12^2+QP^2](https://img.qammunity.org/2021/formulas/mathematics/middle-school/htiziy37ix79990kzk8vr3be7ovtrl9mfa.png)
![QP^2=23.5^2-12^2](https://img.qammunity.org/2021/formulas/mathematics/middle-school/cq8dzkkg75afml2hpfk7439jksx5ghvh0p.png)
![QP^2=408.25](https://img.qammunity.org/2021/formulas/mathematics/middle-school/sgu2f1vfc6rln8latf4l3arpsiptqqc4lf.png)
![QP=20\ units](https://img.qammunity.org/2021/formulas/mathematics/middle-school/yxub5o5zfz16fg04tv4gkpojp14tsijh73.png)