The sum of all the degrees in a circle is 360 degrees. Knowing this you can make a equation:
(x + 40) + (2x + 60) + (3x + 20) = 360
x + 40 + 2x + 60 + 3x + 20 = 360
(x + 2x + 3x) + (40 + 60 + 20) = 360
Now you must combine like terms This means the numbers with the same variables must be combined...
(x + 2x + 3x) + (40 + 60 + 20) = 360
x + 2x + 3x = 6x
(6x) + (40 + 60 + 20) = 360
Now combine the terms without variables (on the left side of the equation) together
(6x) + (40 + 60 + 20) = 360
40 + 60 + 20 = 120
(6x) + 120 = 360
Now we must isolate x. To do this first bring 120 to the right side by subtracting 120 to both sides (what you do on one side you must do to the other). Since 120 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.
6x + 120 - 120 = 360 - 120
6x + 0 = 240
6x = 240
To further isolate x you must divide 6 to both sides. Since x is being multiplied by 6 you must divide 6 to both sides to make 6 one on the left side and bring it over to the right side
6x / 6 = 240 / 6
1x = 40
x = 40
Check:
(40 + 40) + (2(40) + 60) + (3(40) + 20)
(80) + (80 + 60) + (120 + 20)
80 + 140 + 140
360
Hope this helped! Let me know if you have any further questions or want anything clarified.
~Just a girl in love with Shawn Mendes