Answer :

f(X)=4x+12-5=4x+7
so
{f(x)-7}/4=x
now in inverse func. f(x0 is converted into x and x is converted into
f(x)^-1
so
f(x)^-1=[x-7]/4
now if x=3
f(3)^-1=[3-7]/4=-4/4=-1

konrad509
[tex]f(x)=4(x+3)-5\\ y=4(x+3)-5\\ y=4x+12-5\\ y=4x+7\\ 4x=y-7\\ x=\frac{1}{4}y-\frac{7}{4}\\ f^{-1}(x)=\frac{1}{4}x-\frac{7}{4}\\ f^{-1}(3)=\frac{1}{4}\cdot3-\frac{7}{4}\\ f^{-1}(3)=\frac{3}{4}-\frac{7}{4}\\ f^{-1}(3)=-\frac{4}{4}\\ f^{-1}(3)=-1[/tex]