Answer: $75,000 higher over the 15 year period.
Step-by-step explanation:
Current year ending inventory using LIFO = $375,000
Current year ending inventory assuming FIFO was used = $450,000
If Wheat Company had used the FIFO inventory method, there will have been a difference of ($450,000 - $375,000) = $75,000 in pre-tax income over the 15 years period.
Therefore, if Wheat Company had used the FIFO inventory method, pre-tax income would have been $75,000 higher over the 15 year period.