Answer:
21 hours
Step-by-step explanation:
You want to find x such that B(x) = 31. Fill in the value and solve.
... 31 = 1.33e^(0.15x)
... 31/1.33 = e^(0.15x) . . . . divide by 1.33
... ln(31/1.33) = 0.15x . . . . take the natural log
... ln(31/1.33)/0.15 = x ≈ 20.992 . . . . hours
After 21 hours, the concentration will be 31 M/mL.
