(n+20)*2 = 99.2
distribute
2n + 40 = 99.2
subtract 40 from each side
2n = 59.2
divide each side by 2
n = 29.6
In this problem, you must use SohCahToa which basically means:
Sin - opposite over hypotenuse
Cosine - adjacent over hypotenuse
Tangent - Opposite over hypotenuse
So in this picture we have 4 -which is on the opposite side of x - and a 5 -which is the hypotenuse of the triangle. This means we must use sin.
Using a calculator you put in:

Your answer is 53.13 degrees
9) 0.31
10) (7x10^6)-(3x10^3)
7000000-3000=6997000
6.997x10^6
Hope this helps :)
It could be in meters or centimeters according to how long the desk is. But it's usually meters because cm is short