This is a classic tenders question. In contract law one of the types of offer situation you will experience are competitive tenders. There is of course the bilateral contract to award the work to the chosen party. However, that is not the interesting aspect of this area. Tenders are interesting because they may on occasion constitute unilateral offers i.e. NSC makes an offer to consider bids and as a a unilateral offer it is accepted by performing the terms of the offer. This is what we call the 'two contract analysis' from the Blackpool case. Your key reference points here should be Blackpool, Harvela Investments and ensure you identify the narrow legal issue relating to whether a bid which is submitted in a blind tender that adds 'plus' an extra amount can be accepted. A very interesting case.
Don't forget to deal at the end about damages. This is an area which is unclear. If one of the parties has conformed to the conditions set to have their tender considered or accepted and it has not, the NSC will be in breach. The interesting question then becomes what measure of damages is available? None, if it can be shown the injured party would not have been chosen, the contract price if they were a certainty or maybe somewhere in between.