To find how long it will take Tracy to save enough money to buy the guitar, you can set up an equation based on her current savings and her weekly savings.
Tracy has already saved $136.27, and she needs to save a total of $253.77. The amount she still needs to save can be represented as:
\[ 253.77 - 136.27 \]
Now, if she saves $23.50 each week, then the total amount she will have after \( w \) weeks is represented as:
\[ 136.27 + 23.50w \]
To find out how long it will take her to save enough for the guitar, we set the equation:
\[ 136.27 + 23.50w = 253.77 \]
Thus, the correct equation to use to find out how long it will take to save for the guitar is:
\[ \boxed{136.27 + 23.50w = 253.77} \]