1) P = (x + 4x) * 2 = 30
5x * 2 = 30
5x = 30 : 2
5x = 15
x = 15 : 5
x = 3 - вторая сторона
2) 3 * 4 = 12 - первая сторона
3) S = a * b
S = 12 * 3
S = 36
