First, you would subtract $42.95 - $15.99 to get the price markup which is $26.96
Next, put it into a proportion to find out the percentage markup.
part/whole = %/100
26.96/15.99 = x/100 (Based on the cost to make)
x = 168.61%
or
26.96/42.95 = x/100 (Based on selling cost)
x = 62.77%