3a) So you need to calculate the total energy loss i.e the difference energy between A and B.
The 2 types of energy involved are KE and PE. KE is simply 1/2 mv^2 while PE = mgh.
Now consider B as the origin (h = 0 at B)
Now calculate the height at A (the vertical distance between A and B): 14sin20 (basic trig and similar triangle)
KE at A = 1/2 * 3.5 * 12^2
PE at A = 3.5 * 9.8 * 14sin20
KE at B = 1/2 * 3.5 * 8^2
PE at B = 0 (since height = 0)
Now loss in energy = KE at A + PE at A - KE at B