If she starts with 55000 per year, and she get 1700 per year extra, after fifteen years this extra will be 1700*15, or 25500. Add this to her original salary of 55000 per year to get $80500.
You could draw a pie graph, I'm assuming you know how to draw one but I'll tell you anyways. draw a circle with sixty slices, like pizza. shade in 15 percent, or nine sclices. that's my favorite way to model percentages.