A colony of bacteria has 6.5 X 10^6 members at 8 A.M. and 9.75 X 10^6 members at 10:30 A.M. Find its population at noon.

I used the formula N = No X 2 ^ t/d

9.75 X 10^6 = 6.5 X 10^6 X (2)^ 2.5/d

how do i work from here?