Answer:
x = 5.5
m∠AEC = 12.5
Explanation:
m∠AEC = 5x - 15
(to clear up any confusion as it looks like there may be, m∠ simply means angle and is not a variable or anything)
Because these are vertical angles we know they have equal angles therefore, 5x - 15 = 3x + 7
This gives you your first answer, equation needed to solve for x.
Now we want to move our variables to one side and constants to another.
5x - 15 = 3x + 7
5x - 3x - 15 = 7
5x - 3x = 15 + 7
Now we solve,
5x - 3x = 22
2x = 11
x = 5.5
Now we plug "5.5" into the equation "5x - 15"
5(5.5) - 15
27.5 - 15
12.5
m∠AEC = 12.5
REMEMBER TO ALWAYS COMPLETE THE SAME CHANGE TO BOTH SIDES i.e. if you subtract one side by 7 you must also subtract to another
Have a good day and feel free to ask any other questions.