Cost of an oil change: $18.00; Markup: 3/4 answers

I am assuming that the cost of an oil change already includes the mark-up.

So, 18 is 175%. 18 : 1.75 = 10.29 is the original cost.

10.29 * 3/4 = 30.87/4 = 7.71 mark-up

10.29 + 7.71 = 18

Or if 18 is the basis of the mark-up, then,

18 * 3/4 = 54/4 = 13.50 mark-up

18 + 13.50 = 31.50 new cost of an oil change