1. Let $f$ be defined by f(x)={3−x if x≤3,−x3+2x2+3x if x>3.Calculate $f^{-1}(0)+f^{-1}(6)$.
2. For how many values of $x$ is the function $y=\frac{x-2}{x^2-7x+10}$ not defined?
3. If $\sqrt{5 + x} + \sqrt{20 - x} = 7$, what is the value of $(5 + x)(20 - x)$?