[Alex B]

Suppose the concentration of phosphate in Phoenix tap water is 7.3 ppm (mass based), then what is the concentration of selenium in milligrams per liter? The density of water is 1 g/mL. The answer units are mg/L.

I honestly don't even know where to start. I don't see where in the information stem that I could get selenium. Maybe it's just a typo and I'm trying to find the conc. of phosphate....not too sure. Please help by showing all the steps, or by guiding me in the right direction. Thanks!

[AWK]

This is an evident printing error. Probably you should  recalculate selenate SeO_42- (not phosphate) content into selenium Se content in ppm. In this case answer can be about 4 ppm (mg/L)