Find the number that makes the ratio equivalent to 1: 6.
9: __

54



Explanation:

The first ratio is 1:6. The jump from 1 to 6 has us multiplying the 1 by 6 to get 6. 
1*6 = 6
So we follow the same rule of "multiply by 6" to go from 9 to 54 (9*6 = 54)

Or you can use a proportion to get
1/6 = 9/x
1*x = 6*9 ... cross multiply
x = 54
and we get the same answer

The answer is part a: use

The first one is correct