42. Solving a chemistry problem

90. To determine the content of bromide ions, a 100 ml sample of water was titrated with 0.01 N. silver nitrate solution in the presence of sodium chromate as an indicator. 3.1 ml of titrant was used for titration. Determine the content of bromide ions in water (mg/l).
Write down the equation of the ongoing reaction;
Specify the volume of the aliquot, working solution, type of titration.
What is titration, how long does it take?