Ответ:

Q 1+Q2=Q3

cm * 1(t - t * 1) + cm * 2(t - t * 2) =cm3(t3-t)

m * 1(t - t * 1) + m * 2(t - t * 2) =m3(t3-t)

20(t - 18) + 6(t - 42) = 4(72 - t)

10t - 180 + 3t - 126 = 144 - 2t

15t = 450

t = 30

Ответ: 30С