An exterior angle of a triangle is equal to the sum of the two interior angles that are opposite:

d° = b° + c°

To find angle c, remember that the sum of the interior angles of a triangle is 180°:

180° = a° + b° + c°
c° = 180° - a° - b°
c° = 180° - 64° - 42° = 74°

So, d° = 42° + 74° = 116°

A shortcut to get this answer is to remember that angles around a line add up to 180°:

a° + d° = 180°
d° = 180° - a°
d° = 180° - 64° = 116°

A line on the coordinate grid can be defined by a slope-intercept equation: y = mx + b. For a given value of x, the value of y can be determined given the slope (m) and y-intercept (b) of the line. The slope of a line is change in y over change in x, \({\Delta y \over \Delta x}\), and the y-intercept is the y-coordinate where the line crosses the vertical y-axis.

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

To solve this equation, repeatedly do the same thing to both sides of the equation until the variable is isolated on one side of the > sign and the answer on the other.

-7c + 8 > -1 + 7c
-7c > -1 + 7c - 8
-7c - 7c > -1 - 8
-14c > -9
c > \( \frac{-9}{-14} \)
c > \(\frac{9}{14}\)

The area of a rectangle is equal to its length x width:

a = l x w
a = a x b
a = 7 x 9
a = 63