You win your state lottery. The lottery officials offer you the following options: you can accept annual payments of $50,000 for 20 years or receive...

You win your state lottery. The lottery officials offer you the following options: you can accept annual payments of $50,000 for 20 years or receive an upfront payment of $600,000. Ignoring issues like mortality tables, taxes, etc.; and assuming the first payment is made immediately, what market interest rate would make it more attractive to take the upfront payment? 

Please help!!