What are the lengths of the base and height of the pennant?

The base of the pennant is 12 feet shorter than the height ... A = (1/2) * b * h

80 = (1/2) * (h - 12) * h

160 = h^2 - 12h

12/2 = 6

6^2 = 36

h^2 - 12h + 36 = 160 + 36

(h - 6) ^2 = 196

h - 6 = 14

h = 20

b = 8