Question 364110
Given: 
The sum of the measures of all interior angles of a pentagon is 540

345   = the sum of the  measures of the first three interior angles 

345/3 = the mesure of the fourth angle 
      = 115

Let x = the measure, in degrees, of the fifth angle

      = 540 - 345 - 115
      = 80

The measure of the 5th angle is 80 degrees