Physics test tomorrow!!! I NEED HELP!!! inelastic collisions?

Two automobiles of equal m approach an intersection. One vehicle is traveling with velocity 15.0 m/s toward the east and the other is traveling north with speed v2i. Neither driver sees the other. The vehicles collide in the intersection and stick together, leaving parallel skid marks at an angle of 54.5� north of east. What was the initial speed of the northward-moving vehicle?