In the diagram, cd is tangent to the circle, ab = 6 in, and bd = 10 in. find ad.

The complete question in the attached figure

we know that
AB=6 in-----> this is the radius of circle
BC=AB-----> 6 in
AC=12 in-------> is the diameter of circle
BD=10 in

in the right triangle BCD
Applying the Pythagoras theorem

BD²=BC²+CD² --------> CD²=BD²-BC²-----> CD²=10²-6²----> CD²=66
CD=√66 in

in the right triangle ACD
AD²=AC²+CD²-----> AD²=12²+(√66)²----> AD²=144+66----> AD²=210
AD=√210 in-----> AD=14.49 in

the answer is
AD is 14.49 in