If original quantity is 15 and a new quantity is 24 what is the percent increase

Assuming the 15 and 24 is dollars,

To find Markup % use the following equation

Markup%=Markup/Cost*100

and

Markup=Selling Price-Cost

Markup=24-15 = $9

The Markup is now $9

Now, Markup% = 9/15

=0.6*100

=60

Thus, the markup was 60%.