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

c + x = 4
x = 4 - c

then substitute the result (4 - 1c) into the second equation:

-7c + 8(4 - c) = 6
-7c + (8 x 4) + (8 x -c) = 6
-7c + 32 - 8c = 6
-7c - 8c = 6 - 32
-15c = -26
c = \( \frac{-26}{-15} \)
c = 1\(\frac{11}{15}\)

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.

A circle is a figure in which each point around its perimeter is an equal distance from the center. The radius of a circle is the distance between the center and any point along its perimeter. A chord is a line segment that connects any two points along its perimeter. The diameter of a circle is the length of a chord that passes through the center of the circle and equals twice the circle's radius (2r).

An acute angle measures less than 90°, a right angle measures 90°, and an obtuse angle measures more than 90°.

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

a = ½bh
a = ½ x 7 x 3 = \( \frac{21}{2} \) = 10\(\frac{1}{2}\)