$\left[10-\left(-2\right)\right]-\left[5-\left(12\right)\right]+\left[1+\left(6-9\right)\right]$

$56+10k=6\left(7k-12\right)$

$\left(20a+3b+3c\right)-\left(18a+12b-5c\right)$

$-6mn+5mn-3x^2-4x^2$

$2x^2-24z-4+0$

$cos\left(x\right)\frac{dy}{dx}-tan\left(x\right)y=7tan\left(x\right)$

$90^4$