To multiply monomials, multiply the coefficients (the numbers that come before the variables) of each term, add the exponents of like variables, and multiply the different variables together.

(8a)(2ab) + (9a²)(3b)
(8 x 2)(a x a x b) + (9 x 3)(a² x b)
(16)(a¹⁺¹ x b) + (27)(a²b)
16a²b + 27a²b
43a²b

To multiply binomials, use the FOIL method. FOIL stands for First, Outside, Inside, Last and refers to the position of each term in the parentheses:

(y + 3)(y - 9)
(y x y) + (y x -9) + (3 x y) + (3 x -9)
y² - 9y + 3y - 27
y² - 6y - 27

Angles around a line add up to 180°. Angles around a point add up to 360°. When two lines intersect, adjacent angles are supplementary (they add up to 180°) and angles across from either other are vertical (they're equal).

A quadrilateral is a shape with four sides. The perimeter of a quadrilateral is the sum of the lengths of its four sides.

The sum of the interior angles of a triangle is 180°:
180° = a° + b° + c°
c° = 180° - a° - b°
c° = 180° - 51° - 26° = 103°