Answer
x = √45 (irrational so left as a surd)
y = 10
Explanation
Since these are both right angled triangles, you can use the pythagorean theorem: a^2 + b^2 = c^2
6^2 + 3^2 = x^2
36 + 9 = x^2
45 = x^2
x = √45
(3 + 5)^2 + 6^2 = y^2
8^2 + 6^2 = y^2
64 + 36 = y^2
100 = y^2
10 = y