In the diagram, ab = 3 in. and bd = 5 in. if / is tangent to /. points a, b, and c are collinear and a rests on the edge of the circle. find ad.

You've certainly tried hard to describe it in enough detail so that
it can be answered without seeing the diagram.  Sadly, it's not
enough. 

We still don't know what's tangent to what, where point 'C' is, or
how any of this relates to a circle.  You'll have to figure out some
way or us to see the diagram.

2160ft^3 i think you could use a formala to you out with this in the future