5 + x - 14 = -15. Solve for X

Iam so stuck. what is the worked out answer for this question?

Refer to interactive solution 17.45 to review a method by which this problem can be solved. the fundamental frequencies of two air columns are the same. column a is open at both ends, while column b is open at only one end. the length of column a is 0.504 m. what is the length of column b?

Need solving this second acceleration problem.