Basically you want to find an equivalent fraction for 3/5 in the answer choices.
12/20 equals 3/5 because 3/5 x 4/4 (or 1) = 12/20
answer: 4
Let's call this unknown number, x.
So we know that 4 and this number, x, are going to be added together and 6 is going to be subtracted from it. Therefore we can write the expression:

Since we cannot proceed any further without knowing either the value of x or what the expression equals, this is as simplified as it can be.
jus go on the other side of the graph.