Capital Gains

The assessee is an owner of a building where in first 2 floors are used for commercial business and 3rd floor is used as residence by the assessee. Now the assessee has sold the entire property for a consideration in the ratio of 80% for commercial and 20% for residential. The assessing officer has raised a query that the 20% consideration Received is less than the agreement stamp duty valuation. In totality the consideration Received is far more. What remedy can be suggested on this?