Those answers look good to me so I don't quite understand why your teacher wants more. If the questions required a long answer, then it's not unusual for a lot of working to be required but these only take a line anyway. There's a story (which probably isn't true) that a Cambridge undergraduate was awarded a 'first' for a one line answer in the final exam because it was a new and potentially genius way of doing the problem.
Here's a model answer giving all the steps:
In your area of squares and rectangle questions:
Hope that helps,
Bob
]]>What is the area of the circle if the radius is:
1. 4
16*pi
2. SQRT(3)
3*pi
3. 7
49*pi
4. 6x
36 x^2 * pi
5. 10
100*pi
What is the radius if the area of the circle is:
6. 9(PI)
3
7. 4x^2(PI)
2x
8. 25(PI)
5
9. 81(PI)
9
10. 5(PI)
sqrt 5
11. (9/16)PI
3/4
12. 25y^2(PI)
5y
13. 16z^2(PI)
4z
14. t^2(PI)
t
15. t^2(PI)
1
What is the area of the sector if the radius is 6 and the degree measure is:
16. 26
2.68*pi = 9.523
17. 30
3*pi
18. 50
5*pi
19. 90
9*pi
20. 120
12*pi