幫忙解答變分題目

(3x+y):(5x-y) = 17:15
15(3x+y) = 17(5x - y)
45x + 15y = 85x - 17y
40x = 32y
x/y = 32/40
x : y = 4 : 5
(a-b):(b-2a) 2:3
3(a-b) = 2(b-2a)
3a - 3b = 2b - 4a
7a = 5b
a : b = 5 : 7