I need Help plssssssssss

A 1 kg ball moving at 2 m/s perpendicular to a wall rebounds from the wall at 1.5 m/s . The change in the momentum of the ball is:
a) 0.5 N.s away from wall b) 0.5 N s toward wall c) 3.5N s away from wall d) 3.5N s toward wall
The right answer is ( c) but when i try to solve it i get (a)
Change in momentum= M2-M1
M1 = 1.0 kg x 2.0 m/s = 2.0 kg*m/s
M2 = 1.0 kg x 1.5 m/s = 1.5kg*m/s
Change in momentum= 0.5 and that's wrong cause i know the right answer is (c)

2)

Assume the ball's initial velocity is +; (toward the wall)

dP = P2 - P1 = (-1.5) - (+2.0) = -3.5 kg∙m/s (away from the wall)

The catch here is that P2 is negative

Remember, the wall has to provide enough force to stop the ball (2N) and enough to accelerate the ball away from it again (1.5N).
Or to put it another way M1 is in the opposite direction to M2, so if M1 is positive M2 is negative or vice versa.