In this case, our triangle has adjacent side length 4, and hypotenuse of 5. Perhaps it would help if you sketched it!
Using pythagorus, you can work out the length of the side opposite the triangle.
So it's a 3,4,5 triangle! Again, from basic trigonometry, you can calculate :
So now you know sinA and cosA.
a) You need . Remember . You know both!
b) You need . Remeber that . And remember that .
c) You need . Remember . You worked out before, you just need . Use the same concept of: