V = a ^ 3
V= 5 ^ 3 = 125 cm cube
7, 14 would be it but you have to divide the whole equation by 2 to get the y alone
In plain and short, what's 2/3 of 7/8? well, is just their product.
12:15 does not belong, since that is a ratio of 4:5, whilst the others are all 3:4.