Simple,
to find the rate of selling price price based on cost....-rate of cost+rate of the markup..
In work..
S%=C%+M%
The cost is $60 and C is 100%, also you know M%=15%
S%=100%+15%=115%
Rate of the selling price=115%
Step 2: Find the selling price
S=S%*CS=115%*$60S=1.15*60=$69
The selling price at a 15% markup is $69.
Thus, your answer.