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

-a + z = -4
z = -4 + a

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

6a + 7(-4 + a) = 9
6a + (7 x -4) + (7 x a) = 9
6a - 28 + 7a = 9
6a + 7a = 9 + 28
13a = 37
a = \( \frac{37}{13} \)
a = 2\(\frac{11}{13}\)

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 multiply monomials, multiply the coefficients (the numbers that come before the variables) of each term, add the exponents of like variables, and multiply the different variables together.

(3a)(6ab) - (9a²)(3b)
(3 x 6)(a x a x b) - (9 x 3)(a² x b)
(18)(a¹⁺¹ x b) - (27)(a²b)
18a²b - 27a²b
-9a²b

Parallel lines are lines that share the same slope (steepness) and therefore never intersect. A transversal occurs when a set of parallel lines are crossed by another line. All of the angles formed by a transversal are called interior angles and angles in the same position on different parallel lines equal each other (a° = w°, b° = x°, c° = z°, d° = y°) and are called corresponding angles. Alternate interior angles are equal (a° = z°, b° = y°, c° = w°, d° = x°) and all acute angles (a° = c° = w° = z°) and all obtuse angles (b° = d° = x° = y°) equal each other. Same-side interior angles are supplementary and add up to 180° (e.g. a° + d° = 180°, d° + c° = 180°).

The entire length of this line is represented by AD which is AB + BD:

AD = AB + BD