Since A and B are the midpoints of the legs,  is the median of the trapezoid.

The measure of the median of a trapezoid is one-half the sum of the measures of the bases.

So,

              (Substitute )

      (Distributive property)

                         (Simplify)

                               (Add: )

In a trapezoid consecutive interior angles are supplementary.

Find .

         (Consecutive interior angle theorem)

             (Substitute )

                          (Subtract 120 from each side)

Find .

           (Consecutive interior angle theorem)

                 (Substitute )

                         (Subtract 45 from each side)

The measure of AB is 16. and .