Explanation:
It is given that the total units of polymixn B silfate are present as follows.
       (10 + 250) ml = 260 ml
Therefore, total volume necessary to inject the whole volume is as follows.
       [tex]260 \times 15[/tex] drops
        = 3900
It is given that total time required to inject the solution is 2 hours. Converting it into minutes as follows.
           [tex]2 hrs \times \frac{60 min}{1 hr}[/tex]
            = 1200 minutes
Hence, rate of injection is calculated as follows.
   Rate of injection (r) = [tex]\frac{\text{total drops}}{\text{total time}}[/tex]
          r = [tex]\frac{3900}{120}[/tex]
           = 32.5 drops/min
Thus, we can conclude that the rate of injection is 32.5 drops/min.
