Question

F(x) = |2x-3|

find f(x) = 15

Answer 1

15=|2x-3|

then you take the absolute value sign away

(1) 15=2x-3

and

(2) -15=2x-3

you have a negative 15 because it is the absolute value then you solve for both equations
and get
(1) x= 9
(2) x= -6