Multiply: $\left(\frac{1}{5}-\frac{1}{4}y\right)$ and $(5x^2-4y^2)$

We have
$\left(\frac{1}{5}x-\frac{1}{4}y\right)\times (5x^2-4y^2)$
$=\frac{1}{5}x\times (5x^2-4y^2)-\frac{1}{4}y\times (5x^2-4y^2)$
$=\frac{1}{5}x\times 5x^2-\frac{1}{5}x\times 4y^2-\frac{1}{4}y\times 5x^2+\frac{1}{4}y\times 4y^2$
$=x^3-\frac{4}{5}x{y}^2-\frac{5}{4}{x}^{2}y+y^3$