Is set n closed under multiplication, n{all numbers of the form 2^n, for n a natural number}? if so what are the steps to prove it?

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?

Witch represents the inverse of the function f(x)=1/4x-12

Find the value of x. round the length to the nearest tenth