“If the managers’ estimates of the sportswear division’s future free cash flows are realistic, then the valuation using free cash flows ($331·4m) exceeds the current valuation ($585m – $351m = $234m).”
Why did they minus to get the current valuation of $234m?
585 is the value of the company before demerging the sportswear division, and the question says that after demerging the value will be 351. So the value of the sportswear division must be the difference.