I'm going to suggest that we take these and "UN-simplify" them.
For each choice, divide the numerator by 3 and the denominator by 8.
Look at this:
A). 6/14
6 ÷ 3 = 2
14 ÷ 8 = 1.875 ===> 2/1.875 not interesting
B). skip B for just a second
C). 4/9
4 ÷ 3 = 1.33
9 ÷ 8 = 1.125 ===> 1.33/1.125 not interesting
D). 15/35
15 ÷ 3 = 5
35 ÷ 8 = 4.375 ===> 5/4.375 not interesting
But now look at choice-B:
B). 9/24
9 ÷ 3 = 3
24 ÷ 8 = 3 ===> 1/1 interesting !
-- To simplify 9/24, the top and bottom were divided by 3, giving 3/8.
-- To UN-simplify 3/8, the top and bottom were multiplied by 3, giving 9/24.
-- Choice-B is the one that's equivalent to 3/8.
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OK. All of that wasn't really necessary.
All you really need to do is take each choice and simplify it.
A). 6/14
Divide top and bottom by 2 ===> 3/7
B). 9/24
Divide top and bottom by 3 ===> 3/8
C). 4/9
Can't be simplified. Already in simplest form.
D). 15/35
Divide top and bottom by 5 ===> 3/7