To solve for the age of Sarah's sister using the information given:
- We know that Sarah's age (which is 15) is five less than twice her sister's age.
- If we let the sister's age be represented by \( x \), we can write the relationship as follows:
\[ 15 = 2x - 5 \]
Rearranging this equation to solve for \( x \) (the age of Sarah's sister) leads us to the correct initial equation from the provided options.
The equivalent equation you could use to solve for Sarah's sister's age is:
\[ 2x - 5 = 15 \]
So, the correct answer is:
2 x - 5 = 15