Please explain how to do this! My percentage is supposed to be 50% complete with the class so far, but im only at 35%. Thank you. "Proving Pythagorean theorem"

Answer: 28
Step-by-step explanation:
[tex]\sqrt{8^2} -\sqrt{6^2} =\sqrt{?}[/tex]
[tex]\sqrt{64}-\sqrt{36} =\sqrt{?}[/tex]
[tex]\sqrt{64-36} = \sqrt{?}[/tex]
[tex]? = 64 - 36[/tex]
[tex]? = 28[/tex]