HMMT November 2020 U15

For a real number $r$, the quadratics $x^{2}+(r-1) x+6$ and $x^{2}+(2 r+1) x+22$ have a common real root. The sum of the possible values of $r$ can be expressed as $\frac{a}{b}$, where $a, b$ are relatively prime positive integers. Compute $100 a+b$.