Part b confuses me. It seems to me like there is some information missing that causes me to not be able to do it but the teacher has told me that all the information that I need is there. I'll be able to get part C if somebody can help me out with b).

This is Grade 12 Physics and I haven't taken Calculus yet.

Thanks to anybody who can help me out.

The answers on the sheet are:

Spoiler

a) 40 m/s
b) 15 m/s
c) 43 m/s [20^{o} to the horizon] 1. The problem statement, all variables and given/known data

Thanks in advance for any help that you can give me!