S(x) = -x3 + 6×2 + 288x + 4000, 4 ≤ x ≤ 20 is an approximati…

S(x) = -x3 + 6x2 + 288x + 4000, 4 ≤ x ≤ 20 is аn аpprоximаtiоn tо the number of salmon swimming upstream to spawn, where x represents the water temperature in degrees Celsius. Find the temperature that produces the maximum number of salmon.