Oil leaked from a tank at a rate of r(t) liters per hour. The rate decreased as time passed, and values of the rate at two hour time intervals are shown in the table. Find lower and upper estimates for the total amount of oil that leaked out. L (lower estimate) L (upper estimate) t (h) 4 8 10 r(t) (L/h) 8.8 7.6 6.7 6.2 5.7 5.3