Hey I'm not that good at physics or anything but i'll give it a go...
D=ut + .5 a t^2
60= 0 + 1/2 a 7^2
120 = 49a
a = 2.45 m/s...only slightly different to what you got.
I actually find cramming works best. Not so much for exams when you have a whole years worth of stuff to know but for tests and that cramming works best for me :D