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 a so solve the first equation in terms of y:

a + y = 1
y = 1 - a

then substitute the result (1 - 1a) into the second equation:

-9a - 8(1 - a) = -6
-9a + (-8 x 1) + (-8 x -a) = -6
-9a - 8 + 8a = -6
-9a + 8a = -6 + 8
-a = 2
a = \( \frac{2}{-1} \)
a = -2

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.

7a x 8b = (7 x 8) (a x b) = 56ab

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 equal sign and the answer on the other.

-9c - 5 = \( \frac{c}{9} \)
9 x (-9c - 5) = c
(9 x -9c) + (9 x -5) = c
-81c - 45 = c
-81c - 45 - c = 0
-81c - c = 45
-82c = 45
c = \( \frac{45}{-82} \)
c = -\(\frac{45}{82}\)

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 equal sign and the answer on the other.

-8c + 4 = -4 + c
-8c = -4 + c - 4
-8c - c = -4 - 4
-9c = -8
c = \( \frac{-8}{-9} \)
c = \(\frac{8}{9}\)