question about rates of mass in different reactors

I have a matrix a=[15,-2,-1;-3,18,-6;-4,-1,12] and b=[3800;1200;2350] this question is about reactors. So I'm asked to determine how much the rate of mass input to reactor 3 must ben increased to induce a 10 rise in concentration of reactor 1. Please help.

Also how much will the concentration in reactor 3 be reduced if the rate of mass input to reactor 1 and 2 is reduced by 500 and 250?

Thanks a lot!

[Youssef Khmou]

can you explain what b is and what columns and rows of a represent?