Find the area of the trapezoid ABCD with the bases AB and CD, if: AB = 21 cm, CD = 17, the height BH is 7.

Formula for the area of a trapezoid: 1/2 * h * (a + b).
To find the area of a trapezoid, you first need to find the sum of the bases: AB and CD.
AB (a) = 21 cm (by condition).
CD (b) = 17 cm (by condition).
We get: 17 cm + 21 cm = 38 cm.
Next, you need to find the half-sum of the bases, that is, divide the resulting number by 2.
We get: 38 cm: 2 = 19 cm.
The final step is to multiply all this by the height BH.
BH (h) = 7 cm (by condition).
We get: 19 cm * 7 cm = 133 cm².
Answer: 133 cm² is the area of the trapezoid.