IV. [15 points] A manager at Bi-Lo has counted at the rate at which a cashier is scanning items, r(t). This data is given in the following table: t minutes 0 10 20 30 r(t) items/min 30 20 15 10 30 Estimate r(t) dt using left-hand sums and right-hand sums. (a) At = ( b) n = (c) Left-hand sums: (d) Right-hand sums