Answer
$$x=\frac{5}{2},\:x=-\frac{4}{3}$$
Work Step by Step
Solving by plugging in the given value and then using the quadratic formula, we find:
$$ 6x^2-7x-20=0\\ x_{1,\:2}=\frac{-\left(-7\right)\pm \sqrt{\left(-7\right)^2-4\cdot \:6\left(-20\right)}}{2\cdot \:6}\\ x=\frac{5}{2},\:x=-\frac{4}{3}$$
