Question

The total amount of nitrogen from fertilizer that is washed into a river is 2.558×107 mg per year.
The river flows through the field at a rate of 4.02×108 L per year.

Answer 1

Given that : In 1 yr the mass of nitrogen in liquid (river) is $2.558×10^7$ mg,

and the volume of liquid is $V = 4.02×10^8 L$

concentration =$\frac{mass(mg)}{volume(L)}= \frac{2.558×10^7}{4.02×10^8}$

$=0.557mg/L$