?/8 = 15/? = 24/32

Take the first part:

?/8=24/32
Examine the denominators, since 8=32/4
so for the numerators,what number = 24/4?

For the second part, you will reduce 24/32 to its simplest terms, i.e. look for common factors in the numerator and denominator:
24/32, both 24 and 32 are divisible by 8, so divide numerator and denominator by 8 to get
24/32=3/4

Now proceed to solve
15/?=3/4 as in the first part.