Last Question:
Only force acting down was gravity, where a = -gsin15
The inital velocity is 8 and the inital displacement is 13.
Hence v = -gtsin15 + 8
And s = -0.5gt²sin15 + 8t + 13
Set s = 0 to get t = -1.34025 or t = 7.64833
As t must be positive, the time is 7.65 seconds.