A 0.60kg cart moves at 3.0m/s to the right and catches up to a 0.40kg cart moving at 2.0m/s in the same direction. The carts collide and lock together. While they are in contact, a 0.20N horizontal force from air resistance acts opposite their motion for 0.050s. What is the speed of the joined carts immediately after the collision?
a) 2.40m/s to the right
b) 2.59m/s to the right
c) 2.60m/s to the right
d) 2.50m/s to the right