Custom Transacton Calculation - Commercial Real Estate Invoicing

Hello,

I am trying to create a custom transaction form that will allow me to enter certain variables needed to calculate a real estate fee on a line item. There are 4 variables/fields that are needed for this calculation:

Example
Term (# of Months) - 18
Rent - $20.00/year
Area Occupied - 10,000 SF
Fee Structure - 4%

Area            Rate      Annual Rent
10,000 SF * $20.00 = $200,000

Monthly Rent                             Term   Total Rent       
$16,666.67($200,000/12 months) * 18 =  $300,000.06

Total Rent    Fee Structure        Total Fee
$300,000.06 * 4%        =          $12,000

This calculation is not as complicated as it seems......I'm not very good at explaining things. Here is a short version.

((10,000 SF*$20.00)/12)*18)*4%=$12,000

Will I need to utilze scripting for this calculation or can it been done just using field/column calculations? Looking back at my post, I hope I haven't made this too confusing? Thanks in advance for any help/advice anyone can provide!!