6 In a laboratory culture the number N d of bacteria in thousands at temperature d degrees Celsius is given 90 by the function N d 20 for 4 d 32 The temperature D t at time t hours after start time is given by the function d t 3t 4 for 0 t 14 A d 1 a Write an expression for the number of bacteria in terms of t b Determine the initial temperature and number of bacteria in the culture c Determine the number of bacteria after 6 hours d Determine the number of bacteria after 10 hours