Thank you so much for your time !
1) tan(x) = opposite/adjacent so x = tan-1(opposite/adjacent)
Here we have: x = tan-1(5/20)
You can use the calculator on this site to evaluate this (note that atan is the same as tan-1).
2) sin(angle) = opposite/hypotenuse so sin(45°) = 4sqrt(2)/x or x = 4sqrt(2)/sin(45°)
3) Take the "base" to be the 11cm side. The "height" is then given by 9*sin(63°) cm The area is obtained from (1/2)base*height.