Parallelogram ABCD has base equal to 20 cm and its height is three-fourths its base. What is the area of the parallelogram?

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To find the area of this triangle, we may use Heron's formula:
                          A = sqrt ((s)(s - a)(s - b)(s - c))
where s is the semi - perimeter, a, b, and c are the measure of the sides. 
                                  s = (a + b + c) / 2 = (10 + 10 + 16) / 2 = 18
Substituting this to the equation for area,
                         A = sqrt ((18)(18 - 10)(18 - 10)(18 - 16)) 
                                  A = 48 units²