Помогите решить y=100x+5 y=20x+180 y=минус 7x+21 y=-7-21

1) y = 100x + 5

    y = 20x + 180

2) y = -7x + 21

    y = -7 - 21 = -28

2) -28 = -7х + 21

7x = 21 + 28 = 49

x = 7

1) 100x + 5 = 20x + 180 

100x - 20x = 180 - 5

80x = 175

x =  17580

x = 2целых316

=)..€∫∫