I find the problem confusing because it forces a certain sequence of thought process, and I find I get way beyond these questions and answers rather quickly. I would start with the equation of part B, having already recognized the conversions of percent to decimal and the need to make the acid quantities add up. Doing the problem a different way gets you to the answer in part C without any of these "steps," so going back and trying to fill in the "steps" seems awkward, at best.
Perhaps the attachment here helps.