1.64x - 18 = (3/5)x
1.64x - (3/5)x - 18 = 0
1.64x - (3/5)x = 18
1.64x - 0.6x = 18
(1.64 - 0.6)x = 18
1.04x = 18
x = 18 / 1.04
x = 17.3077