excel formuka please

Dear Financial Adviser, My spouse and I are each 62 and hope to retire in 3 years. After retirement we will receive $5,000 per month after taxes from our employers' pension plans and $1,000 permonth after taxes from Social Security. Unfortunately, our monthly living expenses are \$15,000. Our social obligations preclude further coonomies. We have $1,200,000 invested in a high-grade corporate-bond mutual find. Unfortunntely the after-tax return on the fund has dropped to 3.5% per year. We plan to make annual withdrawals from the fund to cover the difference between our pension and social security income and our living expenses. How many years will the money last