i was not provided a dicount rate. its safe to assume or disregard

Year Operating income M$ Investment M$ 30 Net cash Flow M$ -30 -20 Cum net cash flow M$ -30 0 1 50 70 -50 2 150 500 -350 -400 -60 3 340 4 430 340 430 520 5 520 370 890 Sum You have a working interest in a lease with the operating income and investment profile above. a) What the discounted return on investment (ROI) for this project? d) What is the discounted profit to investment ratio where profit = net cash flow