We find the common factor and reduce the fraction:
10/15 = (10/5) / (15/5) = 2/3
15/20 = (15/5) / (20/5) = 3/4
2/6 = (2/2) / (6/2) = 1/3
2/8 = 1/4
3/12 = 1/4
3/9 = 1/3
4/6 = 2/3
5/15 = 1/3
5/20 = 1/4
6/8 = 3/4
6/9 = 2/3
9/12 = 3/4
So we have 5x+15y=45
simplify and undistribute 5 from both sides
5(x+3y)=5(9)
divide both sides by 5
x+3y=9
multiply both sides by 6
6x+18y=54
if it was 6x+18y then the answer is 54
if it was 6x-18y, then I don't know the answer