2 by 3.5 is the area for the model.
Every 1 is meant to represent 20, so multiply both 2 and 3.5 by 20.
2 * 20 = 40
3.5 * 20 = 70
40 * 70 = 2800 in^2
Every 12 inches is 1 foot so divide 2800 by 12^2 (one square foot), or 144.
2800/144 = 19.44444
Round down because .4 is less than half.
Approximately 19 ft^2