How to calculate this equation without using exel or a financial calculator

Discounted payback: Fluid Communication Ltd. is investing $9,365,000 in new technologies. The company expects significant benefits in the first 3 years after installation (as can be seen by the cash flows), and a constant amount for four more years. What is the discounted payback period for the project assuming a discount rate of 10 percent? B 8.33 4-7 $1,250,000 3 $3,378,911 2 $4,558,721 Years Cash flows 1 $2,265,433