Simultaneous equations:
Makes the 2 equations, solving for A and B.
Let A = Model A and B = Model B
A + B = 14
70A + 55B = 905
70A + 70B = 980
70A = 980 - 70B - rearrange and substitute
980 -70B + 55B = 905
980 -15B = 905
-15B =-75
15B=75
B=5
There are 5 Model B's. So that means there must be 9 Model A's.