An art dealer makes a 17.5% commission on every painting sold. if a painting sold for $1500, what was the commission

A percentage is a number out of 100.  So, 17.5% is really 17.5/100, or 0.175.

To find 17.5% of 1500, you multiply 1500 by 0.175

1500 x 0.175 = 262.5.

The commission is $262.50.