Physics momentum question. pls help?

Question

A ball with an original momentum of +3.5 Kg m/s hits a wall and bounces straight back without losing any of its kinetic energy.
The change in the momentum of the ball is :
a)zero
b)-3.5
c)7
d)3.5
e)-7

Answer 1

Well...momentum is a vector quantity, so if it's travelling in exactly the opposite direction, the final momenum is the same magnitude but different sign.

So it lost all it's original momentum (+3.5) and then gained equivalent -ve momentum (-3.5), so the total change is.....

Answer 2

e