Решение уравнений. 30-х=20, х+1=40, у - 8=7
30-х=20
х=30-20
х=10
х+1=40
х=40-1
х=39
у-8=7
у=7+8
у=15
30-x = 20
-x = 20-30
-x = -10
x = 10
x+1 = 40
x = 40-1
x = 39
y-8 = 7
y = 7+8
y = 15