Perfectly inelastic collision problem

1. The problem statement, all variables and given/known data

A 2000kg car moving east at 10 m/s collides with a 3000kg car moving north. They stick together and move as a unit after the collision, at an angle of 40 degrees north of east and at a speed of 5.22 m/s. Find the speed of the 3000kg car before the collision.

2. Relevant equations
Pi=Pf
mivi + mivi= mfvf + mfvf


3. The attempt at a solution
I tried plugging the numbers in the above equation but it did not work. The textbook gives the answer of 5.59 m/s and I cannot figure it out. Somebody give me some help please.