plz solve and explain this question

You would like to plan for your retirement. Your uncle is offering to give you enough money now so that you invest it at 5% compounded monthly and it grows to what you require when you retire at age 60. Your 20 now. You expect to live until age 90. Inflation will always stay at 0%. You currently receive a salary of $50,000 which meets all of your needs now (no saving left over) and will in the future. Taxes (and all other deductions) are payable at a flat 25% of income. How much does dear uncle have to give you