11: =>15x-15-14x-6<=20x+10+18-12x
=>x-21<=8x+28
=>-7x<=49
=>x>=-7
12: \(\Leftrightarrow20\left(-2x-1\right)+15\left(2x^2-3\right)>=10x\left(5-3x\right)+6\left(4x+1\right)\)
=>\(-40x-20+30x^2-45>=50x-30x^2+24x+6\)
=>-40x-65>=74x+6
=>-114x>=71
=>x<=-71/114