How to calculate capital investment?
Presumably the $\$325K$ represents the sale of the equipment.  It is positive while the purchase of the equipment was shown as $-\$6,000K$ 

The question says $\$500K$, but that there has been depreciation down to zero (also shown in the table five times as $\$1200K$)

The depreciation has led to lower taxes being paid, so tax at a rate of $35\%$ is due on the sale of the equipment, and $\$500K \times (1-0.35)=\$325K$ is the net benefit to the company from the sale