Respuesta :

remember
if f(x)=y then f⁻¹(y)=x


so since f⁻¹(3)=5, f(5)=3, a point is (5,3)
x intercept is 6
so another point is (6,0)
so
the slope between (5,3) and (6,0) is (0-3)/(6-5)=-3/1=-3
ok, so when x=6, y=0
0=-3(6)+b
0=-18+b
18=b

y=-3x+18 is equation
or
f(x)=-3x+18