Answer:
17
Step-by-step explanation:
ABC, which is 9z - 1, and CBD, which is 6z + 58, make up ABD, which is a total of 87 degrees.
in order to find the measurement of ABC, you first need to solve for z.
since ABC and CBD make up ABD, add those measurements and set them equal to 87, which is the measure of ABD.
9z - 1 + 6z + 58 = 87
combine like terms starting with the z terms. (it doesn't matter which like terms you combine first)
9z - 1 + 6z + 58 = 87 ⇒ 15z - 1 + 58 = 87
combine the next set of like terms.
15z - 1 + 58 = 87 ⇒ 15z + 57 = 87
subtract 57 from both sides of the equation. it'll cancel itself out on the left, leaving you with 15z = 30 after subtracting 57 from 87.
divide both sides of the equation by 15.
15z/15 = 30/15 ⇒ z = 2
now, plug in 2 for z in each of your equations for the measurements of ABC and CBD.
ABC = 9z - 1 ⇒ 9(2) - 1 ⇒ 18 - 1 ⇒ 17
CBD = 6z + 58 ⇒ 6(2) + 58 ⇒ 12 + 58 ⇒ 70
now, your measurements are
ABD: 87
ABC: 17
CBD: 70
check your work by adding the measurements of ABC and CBD and setting them equal to ABD, or 87.
17 + 70 = 87
87 = 87
since both sides of the equation are equal to 87, you know that your measurements are correct.
therefore, the measure of ABC is 17 degrees.
