Okay...so since 90 degrees out of 360 is taken out that means that the hemisphere is only 250 degrees. That's only 3/4 of a hemisphere. So, you need to find the volume of the hemisphere as if it were a sphere. Then, you divide that by 2 to get the volume of the hemisphere. Then, you multiply it by 3/4 to get the volume of your sliced hemisphere.

If 2x+y=5, then y=5-2x, so he substituted 5-2x correctly.
x+4x=5x, so he combined like terms correctly.
If 5x-10=10, then 5x=10+10 -> 5x=20, so he subtracted 10 from the right side instead of adding 10 to the right side.
The answer is C.
Here's the correct solution:
Letter, it has just been placed differently. But it is the same answer.
Vanessa is 16. When she was 6, he was 54, ten years later he's 64 and she's now 16.
The area of the countertop is (16-ft x 3-ft) = 48 feet² .
1 foot = 0.3048 meter (rounded)
(1 foot)² = (0.3048 meter)² = 0.0929 meter²
48 feet² = (48 x 0.0929) = 4.459 meter² (rounded)