A parallelogram has a base of 12 and a height of 7. What is its area?

The area of a parallelogram is its base times its perpendicular height: $A=bh=12\cdot7=84$, choice C. The height is the perpendicular distance between the bases, not the length of the slanted side. A parallelogram can be cut and rearranged into a rectangle of the same base and height, which is why the formula is the same as for a rectangle. Choice A ($19$) adds the base and the height. Choice B ($38$) doubles that sum, which is like a perimeter. Choice D ($168$) doubles the correct area, as if the base were multiplied by an extra $2$.