SAT Question cab8f907: Area and Volume answer and explanation with Desmos solution

Choice A is correct. The area, $A$, of a triangle is given by the formula $A=\frac{1}{2}bh$, where $b$ is the length of the base of the triangle and $h$ is the height of the triangle. In the right triangle shown, the length of the base of the triangle is $9$ units, and its height is $4$ units. Substituting $9$ for $b$ and $4$ for $h$ in the formula $A=\frac{1}{2}bh$ yields $A=\frac{1}{2}(9)(4)$, or $A=18$. Therefore, the area of the triangle, in square units, is $18$.