The formula for the area of a triangle of base b and altitude h is A = (1/2)(b)(h).
Here, b = 18 cm and h = 9 cm. Â Thus, the desired area is:
    (18 cm)(9 cm)
A = ----------------------- = 81 cm^2
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This problem gives you more info than is needed to solve it. Â The area of the given triangle is 81 cm^2.