A = B x [C / (C + D)]
The above variables are defined as follows:
"A" is the deferred exploration expense subtraction allowable for the taxable year,
"B" is the total deferred exploration expenses reduced by the amount of deferred exploration expenses subtracted in prior taxable years,
"C" is the number of units of ore or mineral sold during the taxable year from the mine or deposit for which the deferred exploration expenses were incurred, and
"D" is the number of units of ore or mineral remaining at the end of the taxable year to be recovered and sold from the mine or deposit for which the deferred exploration expenses were incurred.
Ariz. Admin. Code § R15-2D-305