I am doing an investment appraisal and have looked at a solution where the person who solved it used the residual value after 5 years as cost of equipment rather than the total cost indicated in the question, why is this?

The question states that the cost of equipment is 34,500,000

Depreciation will be over 7 years straight line to zero

Value of Equipment after 5 years will be 5,500,000

How should depreciation be calculated