Replacement question

I have two windows that need channel balance replacements. The marking on the side says 2740 JJ. The length of the channel without the plastic ends is 28". I have two different angled pictures attached of both ends. Can you suggest which parts to order and if I need anything else to replace these parts. I will have handyman do the work.

Are they sold in sets of 2 or 1 piece? I assume I will need 4 channels for the 2 windows.

Thank you!

Thank you. Would it make sense to order the balances for a slightly higher sash weight perhaps the 2750 instead of the 2740? The builder put in the 2750 and it lasted about 10 years with very little usage of the windows. After about 10 years strings on 2 of the 4 balances broke. The windows also were hard to open and close all the way.