investment appraisal

The minimum value of the revenue will be whatever makes the NPV of the project equal to zero. If the pre-tax revenue is X, then there will be tax payable of 0.3X, and so the net cash inflow will be X - 0.3X = 0.7X. The PV of the inflow will therefore be 0.7X x (2 year discount factor at 10%), and this must be equal to $105,000. You can then divide in order to calculate X.