J.R. S. answered 05/16/20
Ph.D. University Professor with 10+ years Tutoring Experience
I see you corrected the original value of x10-4 g to 2.91x10-4 g. Ok. No problem.
To get ppm, which is the same as mg/L, just convert moles/L to mg/L
For Ba2+:
4.89x10-7 mol/L x 137 g Ba/mol x 1000 mg/g = 0.0670 mg/L = 0.0670 ppm Ba2+ (3 sig. figs.)
For Br-:
9.78x10-7 mol/L x 79.9 g Br/mol x 1000 mg/g = 0.0781 mg/L = 0.0781 ppm Br- (3 sig. figs.)

J.R. S.
05/16/20
Angie G.
Thank you so much!05/16/20