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\begin{array}{c} \mathrm{A}=\dfrac{1}{2} b \times h \\ \mathrm{~A}=\dfrac{1}{2} 3 \times 15 \\ \mathrm{~A}=\dfrac{1}{2} 45 \\ \mathrm{~A}=\dfrac{45}{2}=22.5 \end{array}