If you add 5x to 2x+2 you will get 7x+2. You would set this equation equal to 80, so it would be 7x+2=80. When you solve this you will get 11.1428571429, which can be rounded to 11, 11.1, or 11.14, whichever you prefer.
The x is the variable so you have to find what the equation equals in order too find out what variable x is. 2 x7+2 = 16. So now x = 16