Water is poured into a container that has a leak

Water is poured into a container that has a leak. The mass m of the water is given as a function of time t by m(t) = 9.4t0.8 - 3.6t + 15, with m in grams and t in seconds. What is the greatest mass in kilograms (kg)?

The correct answer is: 0.0508 kg Please show me how you get this answer.