Please show the specific formulas used and all steps for both problems

Problem 1 If an investment opportunity is offered now for $3500, how much must it yield at the end of every year for 6 years to justify the investment if interest is 12%? What is the total value of the investment after 10 years? Problem 2 An underground mine is producing zinc ore at $35/ton, which includes all of its mining and processing costs. If it nets a selling price is $0.60/lb of zinc in the concentrate, what is the cutoff grade of the mine (in % zinc) if none of the variables change and recovery of zinc is 88%