Question: A smokestack deposits soot on the ground with a concentration inversely proportional to the square of the distance from the stack. With two smokestacks 20 miles apart, the concentration of the combined deposits on the line joining them, at a distance x from one stack, is given by
S = (k1/k2) + (k2/(20 - x)2)
Where k1 and k2 are positive constants which depend on the quantity of smoke each stack is emitting. If k1 = 7k2, find the point on the line joining the stacks where the concentration of the deposit is a minimum.