Could I please get help with this to work through it with my son?

Could I Please Get Help With This To Work Through It With My Son class=

Answer :

The answer to this equation is 7.5

4^2 + b^2 = 8.5^2
16 - 72.25 = b
b = 56.25
b = square root of 56.25
Final answer is: 7.5

I hope this helps have a nice day.