The concentration of a drug t t seconds after injection is given by C(t)=5t+1/7t^2+7. C ( t ) = 5 t + 1 7 t 2 + 7 . Graph this function on your calculator. Estimate the time at which the concentration is highest (your answer needs to be correct to at least one place past the decimal point): Hint: Use the maximum option on your calculator.