Given that y = 1 / 2x + A and y = BX-1 / 3 are inverse functions, then a + B =?

Given that y = 1 / 2x + A and y = BX-1 / 3 are inverse functions, then a + B =?

y=1/2x+a.x=2y-2a;y=3-bx
-b=2;3=-2a
b=-2,a=-1.5
a+b=-3.5