When solving an equation with two variables, replace the variables with the values given and then solve the now variable-free equation. (Remember order of operations, PEMDAS, Parentheses, Exponents, Multiplication/Division, Addition/Subtraction.)

The sum of the interior angles of a triangle is 180°:
180° = a° + b° + c°
c° = 180° - a° - b°
c° = 180° - 49° - 31° = 100°

To factor a quadratic expression, apply the FOIL method (First, Outside, Inside, Last) in reverse. First, find the two Last terms that will multiply to produce 10 as well and sum (Inside, Outside) to equal -7. For this problem, those two numbers are -5 and -2. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² - 7y + 10
y² + (-5 - 2)y + (-5 x -2)
(y - 5)(y - 2)

The entire length of this line is represented by AD which is AB + BD:

AD = AB + BD

A parallelogram is a quadrilateral with two sets of parallel sides. Opposite sides (a = c, b = d) and angles (red = red, blue = blue) are equal. The area of a parallelogram is base x height and the perimeter is the sum of the lengths of all sides (a + b + c + d).