Question b, why MC must be equal in each factory to minimize total cost. I don't understand what Question B is asking about.

Arm has two plants that produce Identical output he cost functions are (31: 10 q4q2+q3 and C2=10q 2q +q3 a) At what output levels does the average cost curve of each plant reach its minimum? b) If the rm wants to produce four units of output, how much should it produce in each plant