Suppose it takes x days to complete the task, and C helps B to fix it for y days.

Then x/10+(x-y-2)/15+2/30 =1(1).

x/ 12+y/ 15 = 1(2)

That is 3x-2y=32 (3)

5x+4y=60 (4)

(3)*2+(4), get

1 1x= 124

X= 124/ 1 1。

Because124/11>10.

So there is no solution.