( 3 * x - 20 ) : 5 = 50
3 * x - 20 = 50 * 5
3 * x - 20 = 250
3 * x = 250 + 20
3 * x = 270
x = 270 : 3
x = 90
Проверка: (3 * 90 - 20 ) : 5 = 50
480 : ( 13 - t ) + 20 = 100
480 : ( 13 - t ) = 100 - 20
480 : ( 13 - t ) = 80
13 - t = 480 : 80
13 - t = 6
t = 13 - 6
t = 7
Проверка: 480 : ( 13 - 7 ) + 20 = 100