Amount eaten with 〜分
Grammar Explanation: Amount with 〜分

Sacchan and her friends are tasked with going around and selling excess bananas from her mother’s fruit shop. They offer a banana to a shop owner, and when he eats it, Sacchan says he needs to pay for it. The owner realizes he fell for their trap, but offers to buy a bunch.
- 琴葉:
- 「私
( たちが食( べてる分( も買( うといい」- “You should also buy the amount we're eating.”
- おやじ:
- 「まったく。かなわねぇなぁ。わっはっは」
- “Good grief, I'm outclassed. Wahahah!”
Key Points
食べてる分
( means the amount being eaten食
( べてる is casual for 食( べている.分
( turns that action into a quantity: the portion the girls are eating.
も買
( うといい adds that amount tooも means the shop owner should buy not only the banana he ate, but also theirs.
〜といい gives advice.