Answer
$x=\frac{3}{4}$ or $x=-\frac{7}{9}$
Work Step by Step
We simplify as follows:
$36x^{2}+x-21=0$
$36x^{2}+28x-27x-21=0$
$4x(9x+7)-3(9x+7)=0$
$(4x-3)(9x+7)=0$
$4x-3=0$ or $9x+7=0$
$4x=3$ or $9x=-7$
$x=\frac{3}{4}$ or $x=-\frac{7}{9}$
