Profit is computed as a percentage of Sales. For nonperishable items,
the profit is 40% of the sale price. For perishable items the profit is 25%.
Notice that in the compute block, you must reference the variable Sales with
a compound name (Sales.sum) that identifies both the variable and the statistic
that you calculate with it.
/* Compute values for Profit. */
if department='np1' or department='np2' then profit=0.4*sales.sum;