Step-by-step explanation
We can do the following steps to solve the exercise.
Step 1: We can use the exterior angle theorem to find the value of x. This theorem state that the exterior angle is equal to the sum of the two opposite interior angles.
![d=a+b](https://img.qammunity.org/2023/formulas/mathematics/college/3bmg25t6cd6vxosmo31453skn9n3fsjbx3.png)
Then, we can write and solve for x the following equation.
![\begin{gathered} (7x+10)\degree=(2x+40)\degree+(3x)\degree \\ (7x)\degree+10\degree=(2x)\degree+40\degree+(3x)\degree \\ (7x)\degree+10\degree=(5x)\degree+40\degree \\ \text{ Subtract 10\degree from both sides} \\ (7x)\degree+10\degree-10\degree=(5x)\degree+40\degree-10\degree \\ (7x)\degree=(5x)\degree+30\degree \\ \text{ Subtract (5x)\degree from both sides} \\ (7x)\degree-(5x)\degree=(5x)\degree+30\degree-(5x)\degree \\ (2x)\degree=30\degree \\ \text{ Divide by 2\degree from both sides } \\ ((2x)\degree)/(2\degree)=(30\degree)/(2\degree) \\ x=15 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/5yscgjtm7aqnd0dtbpgnlluo3uecqg366l.png)
Step 2: Find the measure of angle ABD. For this, we replace the value of x into the expression that represents the measure of angle ABD.
![\begin{gathered} m\angle ABD=(7x+10)\degree \\ m\angle ABD=(7\cdot15+10)\degree \\ m\angle ABD=(105+10)\degree \\ m\angle ABD=115\degree \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/nuqpzowmg95p3piao4zy41kpq40bouhdw3.png)
Step 3: Find the measure of angle ABC. Angles ABC and ABD are supplementary angles, that is, they add up 180°. Then, we can write and solve the following equation.
![\begin{gathered} m\angle ABC+m\angle ABD=180\degree \\ m\angle ABC+115\degree=180\degree \\ \text{ Subtract 115\degree from both sides} \\ m\angle ABC+115\degree-115\degree=180\degree-115\degree \\ m\angle ABC=65\degree \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/105n4xgatq31a98622j3mtm1g0nv8lilov.png)
Answer
The measure of angle ABC is 65°.