Hi there!
Since ST is a tangent to the circle, we can use the relationship: tangent squared = external secant segment x entire secant segment.
WORK:
(I will be using x in place of ST)
x^2 = 7(23 + 7)
x^2 = 7(30)
x^2 = 210
x = squareroot(210) or approximately 14.5 inches
Hope this helps!! :)
