For a convex 13-gon, what is the sum of the measures of the interior angles?

It doesn't matter whether it's convex or not. The sum of the interior angles
of any 13-sided polygon is (11 x 180°) = 1,980°.

When rates are expressed as a quantity of 1, such as 2 feet per second or 5 miles per hour, they are called unit rates. if you have a multiple-unit rate such as 120 students for every 3 buses, and want to find the single-unit rate, write a ratio equal to the multiple-unit rate with 1 as the second term.