(a) : Here, we have two parameters
                               Â
y= Number of bacteria
                               Â
t= Time
       so f'(t) usually
indicates the slope but the real meaning here for slope is the
growth or decay of
       bacteria. Its units
are growth or decay of bacteria per an hour
(b) If the supply of nutrients is limited f'(4) will be larger
because there will be more growth here.
    for 4 hours, we can say there will be a
little amount of nutrients so that the bacteria can grow but
    for 15 hours there will be less
nutrients compared to there at 4 hours so the growth is also
less.
