Solution:
7.5 hours x 60 minutes = 450 minutes
450 minutes / 75 minutes = 6 total cycles
It starts with 1 cell then splits into 2, then two split into 4, then again to 8, then plits again to 16, then again 32, then splits again to 64. Think of that every new cell will also split into two cells, not just the one you go in full swing with.
A faster way to compute is 2^6 = 64. So therefore, 1-2-4-8-16-32-64