1)30X+18x^2-15-9x-18x^2+30x=87
51x-15-87=0
51x=15+87
51x=102
x=2
2)28x+14x^2-2-x=14x^2+2x-56x-8
28x+14x^2-2-x-14x^2-2x+56x+8=0
81x+6=0
81x=-6
x=-2/27
3)x^2+5x-50-x^2-3x+6x+18=16
8x-32=16
8x=16+32
8x=48
x=6
4)24x^2+3+56x+7=24x^2-6x-28x+7+93x
24x^2+3+56x+7-24x^2+6x+28x-7-93x=0
0=0