We are looking at the value of x given that m ∠ CDE = x and m ∠ EDF = 3x + 20. We have

We first apply the distributive property of multiplication over addition on the parenthesis term. We will get

We now simplify the term on the left-hand side since we have x and -3x as like terms. We have

Then, we apply the additional property of equality to add 20 on both sides of the equation. We get

We now divide both sides by -2 by division property of equality. Hence, we have

We can summarize the steps as follows
