Radius to the tangent point and the tangent line are perpendicular. So, the triangle formed by these three lines - Radius to the tangent point; - tangent line, and - the line connecting you with the center of the silo is an right-angled triangle. Apply the Pythagorean theorem (R+8)^2 = R^2 + 16^2, R^2 + 16R + 64 = R^2 + 256 ====> 16R = 256-64 = 192 ====> R == 12. Answer. R = 12 feet.