Question 486606
For this you would just use a^2 + b^2 = c^2
10{{{sqrt(3)}}}^2 + b^2 = 20^2
173.2 + b^2 = 400
b^2 = 226.8
b = 15.06 
(15.06)^2 + 10{{{sqrt(3)}}}^2 = 20^2
226.8 ft+  173.2 ft = 400 ft.
400 ft = 400 ft. This does check.
Cleomenius.