A quadrilateral is a shape with four sides. The perimeter of a quadrilateral is the sum of the lengths of its four sides.

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

-7a + z = 6
z = 6 + 7a

then substitute the result (6 - -7a) into the second equation:

-5a - 6(6 + 7a) = 6
-5a + (-6 x 6) + (-6 x 7a) = 6
-5a - 36 - 42a = 6
-5a - 42a = 6 + 36
-47a = 42
a = \( \frac{42}{-47} \)
a = -\(\frac{42}{47}\)

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.

A right angle measures 90 degrees and is the intersection of two perpendicular lines. In diagrams, a right angle is indicated by a small box completing a square with the perpendicular lines.

To combine like terms, add or subtract the coefficients (the numbers that come before the variables) of terms that have the same variable raised to the same exponent.

7a + 6a = 13a