let

x = the number of board feet produced by A

y = the number of board feet produced by B

z = the number of board feet produced by C

A, B,and C can produce 7400 board feet of lumber per day

x + y + z = 7400

A and B together can produce 4700 board fee

x + y = 4700

B and C together can produce 5200 board feet

y + z = 5200

by solving the system of 3 equations

x + y + z = 7400

x + y = 7400

y + z = 5200

we find

x = 2200

y = 2500

z = 2700

A by itself can produce 2200 board feet.

B by itself can produce 2500 board feet.

C by itself can produce 2700 board feet.