You are standing at point b. point b is 16 feet from the center of the circular water storage tank and 15 feet from point a. ab is tangent to o at a. find the radius of the tank

The points A and B and the center O  of the circle form a right angle and AO = radius.
So by Pythagoras
16^2 = 15^2 + AO^2

AO = sqrt (16^2 - 15^2)

AO ( radius) =  sqrt31 =  5,57 feet  answer (to nearest hundredth)

Where is the problem