Question 493725
let f(x)=16, and substitute it into the equation
{{{16=x^2-18x+81}}}
{{{0=x^2-18x+65}}}
factor and get {{{(x-13)(x-5)=0}}}
zero product rule says that one of them, (x-13) or (x-5) must be 0 for this to be true, so set each one = to zero and solve
x=13, x=5
x=5,13
You can then check these by substituting them back into the original equation.