At the beginning of the month, a large warehouse has 20,000 metric tonnes of concrete and it doesn't restock until the beginning of next month. Each construction job needs 900 metric tonnes of concrete from the warehouse. The number of construction jobs for a month is random with a mean of 19 and a standard deviation of 7. Find the expected amount of the concrete in metric tonnes at the end of the month in the warehouse before it restocks

answer is 2900