Here is how I approached the problem.
total rake produced from Nov to Feb is 4X.
There are eight months wherein at the beginning of the month X/2 rakes are shipped
We can represent it as below :
Month...........: 1----2----3----4----5----6----7----8
Rakes stored : -----3X--------2X---------X---------0
If you notice, the business need to pay only on the first 7 months because there is no rakes left in the 8th month.
Another important thing to notice is the average number of rakes stored per month is 2X.
So, total storage cost in dollars,
= 7(2X)(0.1) = 1.4X
Hope this helps
-Shaz