please show work and i will like on excel

You have decided to buy a camp spot at the big lake to use your boat. It will cost $70,000 and you have 15 years to make this work. You are able to place $2,500 in to the account at the end of each year. No balance on year 0. First deposit is on year 1. But, you know that won't get you there. You are expecting some bonds to mature in 6 years. (start the savings account now.. 6 years from now, you will have $$ from bonds). If you can get a 3.5% rate on you account (PYCY)... how much do you need from your bonds to make this work