$\left(\frac{2}{3}\cdot\frac{3}{5}\right)^{-1}$

$+7a-8b+5c-7a+5a-6b-8a+12b$

$54+31+7n^2-\:n^2$

$\frac{7x^4-12x^3+6x^2-4x-7}{x-1}$

$3ln\left(x+1\right)=6$

$\frac{sin\left(x\right)}{\cos\left(x\right)}+\frac{sin\left(y\right)}{cos\left(y\right)}=\tan\left(x\right)+tan\left(y\right)$

$\frac{-24}{-\infty}$