Suppose that a volcano is erupting and readings of the rate r(t) at which solid materials are spewed into the atmosphere are given in the table. the time t is measured in seconds and the units for r(t) are tonnes (metric tons) per second. (use 6 equal subintervals.) t 0 1 2 3 4 5 6 r(t) 2 8 20 38 42 54 60 (a) give upper and lower estimates for the total quantity q(6) of erupted materials after 6 seconds. q(6) = tonnes (lower estimate) q(6) = tonnes (upper estimate) (b) use the midpoint rule to estimate q(6). (use 3 equal subintervals.) q(6) = tonnes