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[6] (20 pts) A car is traveling at 50 mph due south at a point 1/2 mile north of an intersection. Another car is traveling at 40 mph due west at a point 1/4 mile east of the same intersection. At what rate is the distance between the two cars changing? [7] (20pts) A bacteria culture starts with 500 bacteria and grows at a rate proportional to its size. After 3 hours there are 8000 bacteria. Find an expression for the population after t hours. Find the number of bacteria after 4 hours