Jeremy was representing the length of a tightrope and wrote the following expressions.

1. List the lengths with which he was working.

   Hint (a):

   Looking at the above expressions, identify each of the lengths that appear in at least one expression.

   Answer (a):

   $3,9,12,$ and $15$ feet

2. Oops! One of the expressions needs to be corrected. Find the expression that does not match the others when it is simplified. Then write a correct expression to replace it. Only use the lengths Jeremy has.

   Hint (b):

   To begin this problem, find the value of each expression. This will determine which expression needs to be changed.

3. What was the length of the tightrope he was working with?

   Hint (c):

   After part (b), each expression should have the same value. This value is the length of tightrope with which Jeremy was working.