Why is D the correct answer for this multiple choice question?

[EF17xx]

Homework Statement

Homework Equations

Fnet= Δp/Δt
p=mv

The Attempt at a Solution

p (before) = 0.4 x 5 = 2
p (after) = 0.4 x 3 = 1.2
Δp = 0.8
Δt = 0.2
Fnet= Δp/Δt
0.8/0.2 = 4N

Correct answer in textbook is D, I do not understand why?

 

[Orodruin]

Momentum is a vector. It has a direction.

 

[EF17xx]

Thank you that makes sense :)