Angles 8 and 7 are adjacent angles, meaning that their sum is 180 degrees. Knowing this you can make a formula like so...
2x + 15 + 3x = 180
Now you must combine like terms. Like terms are numbers that have matching variables OR are numbers with out variables. In this case the like terms are 2x and 3x, since they both have the variables "x" attached.
2x + 3x = 5x
so...
5x + 15 = 180
Now bring 15 to the left side by subtracting 15 to both sides (what you do on one side you must do to the other). Since 15 is being added on the left side, subtraction (the opposite of addition) will cancel it out (make it zero) from the left side and bring it over to the right side.
5x + 15 - 15 = 180 - 15
5x + 0 = 165
5x = 165
Next divide 5 to both sides to finish isolating x. Since 5 is being multiplied by x, division (the opposite of multiplication) will cancel 5 out (in this case it will make 5 one) from the left side and bring it over to the right side.
5x / 5 = 165 / 5
x = 33
x is 33.
To find measure of angle 7, plug in 33 for x in 2x + 15 and solve
2(33) + 15
66 + 15
81
Measure of angle 7 is 81 degrees
Hope this helped!
~Just a girl in love with Shawn Mendes
