If the number of bacteria triples every 4 hours, then after 1 day (24 hours), the number of bacteria will triple 6 times.
Tripling a number 6 times is the same as multiplying it by 3 raised to the power of 6, or 3^6.
So, if there are 25 bacteria to start, the number of bacteria after 1 day will be:
25 x 3^6 = 25 x 729 = 18,225 bacteria.