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

3c + x = -5
x = -5 - 3c

then substitute the result (-5 - 3c) into the second equation:

-9c + 3(-5 - 3c) = 3
-9c + (3 x -5) + (3 x -3c) = 3
-9c - 15 - 9c = 3
-9c - 9c = 3 + 15
-18c = 18
c = \( \frac{18}{-18} \)
c = -1

The area of a trapezoid is one-half the sum of the lengths of the parallel sides multiplied by the height:

a = ½(b + d)(h)
a = ½(3 + 7)(4)
a = ½(10)(4)
a = ½(40) = \( \frac{40}{2} \)
a = 20

A triangle is a three-sided polygon. It has three interior angles that add up to 180° (a + b + c = 180°). An exterior angle of a triangle is equal to the sum of the two interior angles that are opposite (d = b + c). The perimeter of a triangle is equal to the sum of the lengths of its three sides, the height of a triangle is equal to the length from the base to the opposite vertex (angle) and the area equals one-half triangle base x height: a = ½ base x height.

To solve this equation, replace the variables with the values given and then solve the now variable-free equation. (Remember order of operations, PEMDAS, Parentheses, Exponents, Multiplication/Division, Addition/Subtraction.)

6a(a - x)
6(-2)(-2 - 8)
6(-2)(-10)
(-12)(-10)
120

When solving an equation with two variables, replace the variables with the values given and then solve the now variable-free equation. (Remember order of operations, PEMDAS, Parentheses, Exponents, Multiplication/Division, Addition/Subtraction.)