Discounted Payback Question regular, required, discounted, question, investing

amqata

Hi all, just wondering how you calculate Discounted Payback quickly? Can it be done on the BA II (regular)? As you can fairly quickly get the payback period without much calculation can you go one step further to get the discounted payback?
Anyway the question is from Pg34 of the CFAI Book 4, Corporate Finance, Q6;
Kim Corporation investing 750m won, cash inflows of 175m won per year for 7 years. The required rate of return = 10%. Expressed in years, what is the (payback period &) discounted payback period?