Since we start with 800 mg then we know that 8000P0. It can be expressed by the formula ya1-b x wherein y is the final amount a is the original amount b is the decay factor and x is the amount of time that has passed. Y a 1 -bx.
Exponential growth and decay often involve very large or very small numbers.
Decay exponentially at least for a while. Decay Formula Formula for Half-Life in Exponential Decay large NtN_0left frac12fractt_frac12 right. You can do an exponential equation without a table and going straight to the equation YC 1- rT with C being the starting value the being for a growth problem the - being for a decay problem the r being the percent increase or decrease and the T being the time. In fact t actually represents less than the number of hours required for the amount of drug left to go below 52 mg.