Perimeter is equal to the sum of the four sides:

p = a + b + c + d
p = 7 + 4 + 6 + 9
p = 26

To solve this equation, isolate the variable for which you are solving (a) on one side of the equation and put everything else on the other side.

8a - y = -3a - 5y + 9
8a = -3a - 5y + 9 + y
8a + 3a = -5y + 9 + y
11a = -4y + 9
a = \( \frac{-4y + 9}{11} \)
a = \( \frac{-4y}{11} \) + \( \frac{9}{11} \)
a = -\(\frac{4}{11}\)y + \(\frac{9}{11}\)

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 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.

-5c - 9 = \( \frac{c}{4} \)
4 x (-5c - 9) = c
(4 x -5c) + (4 x -9) = c
-20c - 36 = c
-20c - 36 - c = 0
-20c - c = 36
-21c = 36
c = \( \frac{36}{-21} \)
c = -1\(\frac{5}{7}\)

The circumference of a circle is the distance around its perimeter and equals π (approx. 3.14159) x diameter: c = π d. The area of a circle is π x (radius)² : a = π r².