Question 1104167
<br>Since area is measured in square units, the ratio of areas in similar figures is the square of the scale factor (ratio of linear measurements).<br>
Side length is a linear measurement; if the scale factor is 1:40, the ratio of areas is 1:1600.  If the scale model required 3 gallons of paint, the original figure will require 1600*3 = 4800 gallons.