physics question?

Question

A 2.5 kg cart, moving along the x-axis with constant acceleration, crosses the origin at t=0 with velocity 4.0 m/s to the left. What must be the net force on the cart if some time later it is moving to the right at velocity 12 m/s at position +10 m?
please asap
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Answer 1

12 m/s = - 4 m/s + at
10 m = 0 - 4t + (1/2)at^2
t = 16/a
(1/2)(256/a) - 64/a = 10
10a = 128 - 64
10a = 64
a = 6.4 m/s^2
F = (2.5 kg)(6.4 m/s^2) = 16 N