If 1.5x = 0.04y, then the value of ( (y - x) / (y+x) ) is :

x / y  = 0.04 / 1.5 = 4 / 150 = 2 / 75.

= > ( (y - x) / (y+x) ) = (1 - (x / y)) / ( 1 + ( x / y)) = (1 - 2/75) / (1 + 2/75) = 73/77...