Can someone help me find the missing x and the 2 Pythagorean’s triples

Below in BOLD.

Step-by-step explanation:

1.  x^2 = 3^2 + 6^2

x^2 = 9 + 36 = 45

x = √45

x = 3√5.

2. 15^2 = x^2 + 12^2

x^2 = 15^2 - 12^2 = 225 - 144 = 81

x = 9.  

9, 10 and 15 are Pythagorean triplets.

3.  x^2 = 10^2 - 6^2 = 64

x = 8.

6, 8 and 10 are Pythagorean triplets.