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6. (7 pts) The work done by stretching a certain spring increases by 0.13x joules per centimeter (where x is the displacement, in centimeters, beyond the spring's natural length). How much work (in Joules) must be done in order to stretch the spring from = 4 to x = 10? Choose 1 answer: © O D 7. (7 pts) 5.46 7.54 10.92 15.08 Consider the following problem: The water level under a bridge is changing at a rate of r(t) = 40 sin centimeters per hour (where t is the time in hours). At time t = 3, the water level is 91 centimeters. By how much does the water level change during the 4th hour? Which expression can we use to solve the problem? Choose 1 answer: r(t) dt πt 6 f*r(t) di © [*7 (8) de Ⓒ[ r(t) r(t) dt