You need to find the value of a so solve the first equation in terms of x:

7a + x = 7
x = 7 - 7a

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

a + 9(7 - 7a) = 5
a + (9 x 7) + (9 x -7a) = 5
a + 63 - 63a = 5
a - 63a = 5 - 63
-62a = -58
a = \( \frac{-58}{-62} \)
a = \(\frac{29}{31}\)

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

-b + 4z = 9b + 2z + 6
-b = 9b + 2z + 6 - 4z
-b - 9b = 2z + 6 - 4z
-10b = -2z + 6
b = \( \frac{-2z + 6}{-10} \)
b = \( \frac{-2z}{-10} \) + \( \frac{6}{-10} \)
b = \(\frac{1}{5}\)z - \(\frac{3}{5}\)

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.

The area of a triangle is equal to ½ base x height:

a = ½bh
a = ½ x 4 x 9 = \( \frac{36}{2} \) = 18

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.