A credit union lends 5m in home loans (with duration of 12.8242 years) and 5m in small business loans (with duration of 8.4847 years). It finances 90% of its lending with deposits (with duration of 4.7623 years) and 10% with retained earnings. Moreover, the credit union has an additional 1m invested in money market instruments with duration zero. What is the duration of the credit union's balance sheet (in years)?