(1 point) A smokestack deposits soot on the ground with a concentration inversely proportional to the square of the distance from the stack. With two smokestacks d miles apart, the concentration of the combined deposits on the line joining them, at a distance z from one stack, is given by where c and k are positive constants which depend on the quantity of smoke each stack is emitting. If k concentration of the deposit is a minimum. 2c, find the point on the line joining the stacks where the Ei mi