Opencart Calculation

Hi,


http://postimg.org/image/jk5xbj6wv/

Hi, i am creating a OpenCart store that sell banners. Based on the picture above, the total price of the banner is the sum of the white & the red areas. I already find an extension that can calculate the white area (extension name: Product Size Option). But i don't know how to calculate the red areas. The red areas are the extra material that clients can choose to add. The clients should choose how many inches of the red area that they want to add, but the anything less 4 inches are free of charge.

Any advice on how can i solve it? Or any extension i can use? \

Thank you.

width_white = 3
height_white = 4

width_red = 2

square_red = (width_red*width_white)*2 + (width_red*height_white)*2

Hi Chulcha,

Thank you for the equation. Do you know how i can implement it on OpenCart?

Describe in more detail.
The width and height of the white block are optional, or option is the area of the square.
The width and height of the red stripes are optional or option is the summary square.

These values can be integer or decimal as well?
These values can be fixed size?

PM?