Use the formula (n - 2) * 180 to find the sum of the interior measures of a polygon.
n stands for the number of sides that the polygon has, so substitute 10 for n since a decagon has 10 sides.
(10 - 2) * 180, start by solving inside the parentheses and subtracting 10 and 2.
(8) * 180, multiply.
B. 1,440 is your answer.