(1)y=3x+5
x=(y-5)/3
f^-1(x) =(x-5)/3
(2)
f^-1(f(x))=f^-1(3x-5)=[(3x-5)-5]/3=x
(3)
f[f^-1(x)]=f[( x-5)/3]=3*[(x-5)/3]-5=x