Chemistry- Balancing in Redox reactions

[Elvina_Erin]

Hi, I’m really facing difficulty in balancing the equation in questions like these. I’m familiar with the formulas and how to calculate them but I can’t balance the equation correctly. Please help me.

[Juliette]

hi
first what is the answer? i found 71,4g and 4 M

[Elvina_Erin]

hey, the answer key provided gives 15g and 0.85M. And i have no idea how to arrive at this answer. Please help