These are all in the form of mixed fractions. So you need to firstly convert them into improper fractions so that you can multiply the numerator and denominator.
1) 17/8 * 15/4
To multiply fractions, multiply both of the top numbers of both fractions (numerator) and multiply both of the bottom part of the fractions (denominator)
17*15=255 (numerator)
8*4=32 (denominator)
Now the question is asking you to ESTIMATE which is closer 6 or 8
So you divide numerator by denominator:
255/32=7.96875
Round this to 8
So your answer to Q1 is 8.
I used this same method for the rest of the questions:
Q2) improper: 32/9*11/9
Solve: 352/81
Divide: 4.34....
Closer to 6
Answer is 6
Q3) improper: 59/8*14/5
Solve: 826/40
Divide: 20.65
Closer to 21
Answer is 21
Q4) improper: 43/9*41/12
Solve: 1763/108
Divide: 16.324...
Closer to 15
Answer is 15
Hope I helped :)