Answer:
M a = (M1 + M2) a = F Newton's Second Law
F = (M2 - M1) g net force on the system
a = (M2 - M1) / (M1 + M2) g
a = (9 - 7) / (9 + 7) g = 2 / 16 * 10.0 m/s^2 = 1.25 m/s^2
