To find the area of a regular hexagon, or any regular polygon, we use the formula that says Area = one-half the product of the apothem and perimeter. As shown below, this means that we must find the perimeter (distance all the way around the hexagon) and the measure of the apothem using right triangles and trigonometry. Area of a Hexagon
I'm pretty sure the answer is D. because I don't think anyone would want to take their total meal cost and then multiply it by their tip to make it even larger. You would just add the tip to the meal cost.
It works because 7 x 9 x 10 is the same thing as 7 x 90, since 9 x 10 is just 90. So basically he is just writing more but the answer will still be the same.
