Angle on straight lines adds to 180. So, 180 - 125 =55. If base angles are equal, to find x, add all vales of y and take away from 180. Angle in triangle add to 180.
To write the equation you start with the 125 because it is monthly and it doesn't say how often you pay the 75 dollars so the equation would be c(f)=125x+75
