Chemistry
posted by Mohammed .
A farmer applies 1400.0 kg of a fertilizer that contains 10.0% nitrogen to his fields each year. fifteen (15.0%) percent of the fertilizer washes into a river that runs through the farm.
If the river flows at an average rate of 0.410 cubic feet per second, what is the additional concentration of nitrogen ( expressed in milligrams of nitrogen per liter) in the river water due to the farmer's fertilizer?

1. Determine the mass of nitrogen that washes into the river each year, in milligrams.
( Multiply the mass of fertilizer by both percentages. )
2. Determine the volume of river that flows through the farm each year, in litres.
( Convert cubic feet to litres, multiply by the number of seconds in a year. )
3. Divide and conquer. 
I know that. I already used these steps, but the answer was wrong.

1: 1400.0 * 10^6 * 0.100 * 0.150 = 2.10E7 mg
2: 0.410 * 28.32 * 3.154E7 = 3.66E8 L
3: 0.574 mg/L 
I'm so sorry for bothering you, but the answer still wrong. It says that this is similar to the amount of fertilizer in the river water, but the amount of nitrogen will be less. So, what percent of the total mass of the fertilizer is nitrogen?
Thanks,