Question 497975
Form the way I interpret this question, the length will range from 39 cm to 15 cm.
The width is constant at 10 cm.
The maximum area will be 39 * 10 or 390 cm.
The minimum area will be 15 * 10 cm or 150 cm.
So the difference will be 390 - 150 or 240 cm. 
Cleomenius.