$3y-4\left(6-y\right)=15-6y$

$6x^2-15^2+21^2$

$\lim_{x\to0}\left(\frac{2ln\left(1+\frac{x}{2}\right)}{x^2}\right)$

$\frac{24xy}{12x}$

$f\left(x\right)=\sqrt{\frac{3x-2}{x+1}}$

$-\left(9a-7b\right)^2$

$\lim_{x\to1}\left(\left(x^2-1\right)\left(\ln\left(x-1\right)\right)\right)$