The base and the altitude of a triangle are (3x – 4y) and (6x + 5y) respectively. Find its area.
Reqd. Area = (base) x (altitude)
= ½ (3x – 4y) (6x + 5y)
= ½ (18x^{2} + 15xy – 24xy – 20y^{2})
= ½ (18x^{2} – 9xy – 20y^{2}) sq. unit.