Since you are having trouble with part (a) I will help you with that part, but you should be able to do part (b) by simple substitution after part (a) is complete.
So first, break the problem into horizontal and vertical components. The horizontal velocity is
The distance traveled will be 12,000 ft, so the time can be found by
Solve for t:
Now the vertical components of the equation are
Substitute for the time and the location of 2000 ft:
Use the substitution that
.
Rearrange the equation:
Solve the quadratic equation above to get:
Solve for α:
Either angle will reach the target.