Stuck on a mechanics problem, help greatly needed!?

Okay so here's the question, exactly as it is worded: "A shopper pushes a supermarket trolley in a straight line towards her car with a force of magnitude 20N, directed downwards at an angle of 15 degrees to the horizontal. Given that the acceleration of the trolley is 2.4ms squared, and neglecting friction, calculate it's mass. Find also the magnitude of the normal contact force (N) exerted on the trolley by the ground." I had a few tries at the problem using my notes from class, but I couldn't seem to do it. Help please! Even if you only know how to find mass, it would be greatly appreciated!