We are given a trapezoid TRHY.
Height of the trapezoid = 13 units.
b1 = 21 units and
Area = 215 units squares.
We need to find the length of b2.
We know formula for area of a trapezoid.

Plugging values in formula.
215 =
(21+b2)× 13.
215 = 6.5(21+b2)
Dividing both sides by 6.5, we get

33.08 = 21+b2.
Subtracting 21 from both sides, we get
33.08-21 = 21-21+b2
b2 = 12.08.
Therefore, length of b2 is 12.08 units.