Write $6+5x-4x^2=0$ in standard form, then solve it with the quadratic formula.

Reversing the order and multiplying by −1 to make a positive: $4x^2-5x-6=0.x=\frac{5\pm \sqrt{25+96}}{8}=\frac{5\pm 11}{8}=2$ or $-\frac{6}{8}=-\frac{3}{4}$. Check: 6 + 10 − 16 = 0, and 6 − 3.75 − 2.25 = 0. Multiplying by −1 changes the sign of every term, so a student who flips only the $x^2$ term gets the signs of the roots wrong.