We can multiply Leroy's hourly wage by the total number of hours he worked. On Friday, Leroy spent a total of (3 1/2 + 2 1/2) hours = 6 hours working. If he earns $11.75 in 1 hour, multiplying this by 6 gives $70.50, so this is the total amount he earned on Friday.
So.. in this case, the starting amount is the 500mg sample... and the rate of decay, negative rate, is 1%, and at the time, the elapsed days is 0, to t = 0, P = 400
