f(x) = (2 - 3x)/4 => f(x) = y:
y = (2 - 3x)/4 => switch x & y:
x = (2 - 3y)/4 => solve for y:
x/1 = (2 - 3y)/4 => now cross multiply:
2 - 3y = 4x => subtract 2 from both sides:
-3y = 4x - 2 => divide both sides by -3:
y = (2 - 4x)/3 => this is the inverse function, so:
f^-1(x) = (2 - 4x)/3