If 2,4,5=3; 3,9,9=6; 4,12,8=5 and 5,10,8=6 then what is 6,18,7=?

Question

If
2,6=5
4,9=7
6,11=8
8,15=11
then
12,18=?

Answer 1

let A, B, C = Y

then, C - (B/A) = Y

Answer 2

The answer is 4. The reason is that if you take the third number and subtract it by the second number divided by the first number, then you get the fourth number. For example, in the first one, 5 - (4/2) = 3. and in the second, 9 - (9/3) = 6.