💡 Detailed Explanation
The speaker is implying they need help because they can't finish the task alone. The most natural response is to offer help. 'じゃあ、半分やりましょうか。' (Then, shall I do half?) is a direct offer of assistance. 'そうですか。大変ですね。' (Is that so? That sounds tough.) is sympathetic but unhelpful. 'ええ、とても終わりそうですよ。' (Yes, it looks like you can finish it.) contradicts the speaker and is uncooperative.