the answers are there,
are there any explnataions u need?
like with part iii of 7b, u know that at 45 degrees, the distance will be greatest
the two values that u have to work out is one where u can throw it at 45 degrees, but the oother, if its throw at 45 degrees, the ball will strike the roof, so u have to work out the angle where the ball won;t hit the roof that is less than 45 degrees that will make the ball go the furthest.
this is done jsut by manipulating the equations u derrived earlier on