We are looking at the value of x given that m ∠ CDE = x and m ∠ EDF = 3x + 20. We have
![\begin{gathered} m\angle CDE-m\angle EDF=180 \\ x-(3x+20)=180,\mleft(Given\mright) \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/iklqpktmqmjjmy822bzymrufv5ssgf482o.png)
We first apply the distributive property of multiplication over addition on the parenthesis term. We will get
![x-3x-20=180,(\text{Distributive Property of Multiplication over Addition})](https://img.qammunity.org/2023/formulas/mathematics/high-school/50rq1sgrhxuz6tmopmox21hn5txhzx7w10.png)
We now simplify the term on the left-hand side since we have x and -3x as like terms. We have
![-2x-20=180,(\text{Simplify})](https://img.qammunity.org/2023/formulas/mathematics/high-school/ucsmsrn1oakze8tokcmuwp341wi46eh3za.png)
Then, we apply the additional property of equality to add 20 on both sides of the equation. We get
![\begin{gathered} -2x-20+20=180+20,(\text{Addition property of equality}) \\ -2x=200,(\text{Simplify}) \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/uhzftrhmo9ewk8w57etr74hcfb9f8xw94g.png)
We now divide both sides by -2 by division property of equality. Hence, we have
![\begin{gathered} (-2x)/(-2)=(200)/(-2),(\text{Division property of equality}) \\ x=-100,() \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/parnx39hpsl742cuhuuqes3brda56pfa0c.png)
We can summarize the steps as follows
![\begin{gathered} m\angle CDE-m\angle EDF=180 \\ x-(3x+20)=180,(Given) \\ x-3x-20=180,(\text{Distributive Property of Multiplication over Addition}) \\ -2x-20+20=180+20,(\text{Addition property of equality}) \\ (-2x)/(-2)=(200)/(-2),(\text{Division property of equality}) \\ x=-100 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/1kw2qwb1wj0tx4lhef1mh61m8t221gc06v.png)