Recall that a variable y satisfies exponential growth if it satisfies the differential equation y ' = k * y (where k > 0). The solution to this differential equation is y = C * e^( k * t ), where C represents the initial value of y at time t = 0. Typically the value of k is found from knowing the value of y at some other time t.
Use this information to solve the following: A bacteria population starts with 4 million bacteria and triples every 30 minutes. How many bacteria are present after 45 minutes?