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° - 70° - 31° = 79°

So, d° = 31° + 79° = 110°

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° - 70° = 110°

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).

You need to find the value of c so solve the first equation in terms of z:

-7c + z = -3
z = -3 + 7c

then substitute the result (-3 - -7c) into the second equation:

-9c - 3(-3 + 7c) = 8
-9c + (-3 x -3) + (-3 x 7c) = 8
-9c + 9 - 21c = 8
-9c - 21c = 8 - 9
-30c = -1
c = \( \frac{-1}{-30} \)
c = \(\frac{1}{30}\)

To combine like terms, add or subtract the coefficients (the numbers that come before the variables) of terms that have the same variable raised to the same exponent.

6a + 7a = 13a

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 + 8)(y - 9)
(y x y) + (y x -9) + (8 x y) + (8 x -9)
y² - 9y + 8y - 72
y² - y - 72