12/15 simplifies to 4/5, whereas all the others simplify to 2/3. Therefore, 12/15 is not equivalent to the rest.
3/1 or just 3. The highest number divisible by the denominator (bottom number) and numerator (top number) is 6, so 18 divided by 6 is 3 and 6 divided by 6 is 1. That gives 3/1, or just write 3.
PEMDAS states that the value in the parenthesis should be evaluated first:
4(5*6)
4(30)
After just multiply the value in the parenthesis by the number outside of the parenthesis:
120
The answer for your question is letter D