a) 3.6 / 4.2 = 6 / x
Умножим обе части уравнения на 4.2:
3.6 = 6 * 4.2 / x
3.6 = 25.2 / x
x = 25.2 / 3.6
x = 7

б) 15 / 10 = x / 40
Умножим обе части уравнения на 40:
15 4 = x 10
60 = 10x
x = 6

в) 3 / x = (3/8) / (1/4)
3 / x = 3/2
3 * 2 = x
x = 6

г) x / (4/3) = 6 / 4
x / (4/3) = 1.5
x = 1.5 * (4/3)
x = 2

д) x / 3.86 = 2.5 / 2.5
x / 3.86 = 1
x = 1 * 3.86
x = 3.86