find [H3O+] and [OH-]

Question

1)a solution that is 5.8×10−2 M in [HBr] and 1.9×10−2M in [NO3].

2)a solution that is 0.780% HNO3 by mass (Assume a density of 1.01 g/mL for the solution.)

Answer 1

(H^+) HBr soln = (HBr)
To find OH, remember (H^+)(OH^-) = Kw = 1E-14

0.780% by mass means 0.78g/100 g soln.
Use density to convert 100 g soln to mL. Convert 0.78 g to mols. That will give you molarity and you can go from there.