с уравнением (1,75+х)*7=30,1

(1,75+х)*7=30,1

12,25 + 7x = 30,1

7x = 30,1 - 12,25

7x = 17,85

x = 2,55

(1,75 + x) * 7 = 30,1

1,75 * 7 + 7x = 30,1

12,25 + 7x = 30,1

7x = 30,1 - 12,25

7x = 17,85

x = 17,85 : 7

x = 2,55

(1,75 + 2,55) * 7 = 30,1

30,1 = 30,1