$$(-\frac{4}{5})x^2+24x-90 = 0$$

$$ \begin{aligned} (-\frac{4}{5})x^2+24x-90 &= 0&& \text{multiply ALL terms by } \color{blue}{ 5 }. \\[1 em]5(-\frac{4}{5})x^2+5\cdot24x-5\cdot90 &= 5\cdot0&& \text{cancel out the denominators} \\[1 em]0+120x-450 &= 0&& \text{simplify left side} \\[1 em]120x-450 &= 0&& \text{ move the constants to the right } \\[1 em]120x &= 450&& \text{ divide both sides by $ 120 $ } \\[1 em]x &= \frac{450}{120}&& \\[1 em]x &= \frac{15}{4}&& \\[1 em] \end{aligned} $$

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