I thought x-7 was the right answer because don't you need to subtract? But apparently it was wrong so then which one is the correct answer?

Answer:
It is 7x-7
Step-by-step explanation:
You have to add the two expressions, not subtract them.
Answer:
no you need to add, it would be 7x - 7
Step-by-step explanation:
You need to look at the line...they gave you the measurement for PR, and the measurement for RS...and they want you to find PS
You need to add because both PR and RS come together to form PS