Find the sum of the measures of the angles in an octagon

Idon’t understand this.. will someone ? will mark brainliest along with 20 points.

The data in the table represent the height of an object over time. which model best represents the data? height of an object time (seconds) height (feet) 05 1 50 2 70 3 48 quadratic, because the height of the object increases or decreases with a multiplicative rate of change quadratic, because the height increases and then decreases exponential, because the height of the object increases or decreases with a multiplicative rate of change exponential, because the height increases and then decreases

What expression is equivalent to (2x-1)(x-3)?