Решил уравнения.
x+31=40
x-75=20
96-x=72
23+x=30

х+31=40x = 40 - 31x = 9x- 75 = 20x = 20 + 75 x = 9596-x=72x = 96 - 72x = 2423+x=30x = 30 - 23x = 7

x+31=40 x-75=20 96-x=72 23+x=30 x=40-31 x=20+75 x=96-72 x=30-23x=9 x=95 x=24 x=79+31=40 95-75=20 96-24=72 23+7=30