Two solutions of different concentrations of acid are mixed creating 40 ml of a solution that is 32% acid. One-quarter of the solution is made up of a 20% acid solution. The remaining three-quarters is made up of a solution of unknown concentration, c. Which equation can be used to determine c, the unknown concentration? 30c + 10(0. 2) = 40(0. 32) (c) + (0. 2) = 40(0. 32) (c)( (0. 2)) = 40(0. 32) 30(c)(10(0. 2)) = 40(0. 32).