The first thing to do is figure out the price after the discount. If it's on sale for 15% off, you take 700*.15 which gives you 105. You then subtract 105 from 700 and this gives you the sale price of $595.
The next thing to do is subtract the amount on the gift card from the price of the violin. To do this you take 595-60 which gives you $535.
And there you have it! After accounting for the 15% off and the $60 gift card, the violin will cost the customer $535.
notice the picture of the graph added here low and behold, x = -17, y is 0, and x= 15, y is 0 the graph is touching the x-axis, an x-intercept or so-called, a "solution"