Using "unless":

• Unless you give me a hand, I can't finish this task.

Using "if":

• If you don't give me a hand, I can't finish this task.
• I can't finish this task if you don't give me a hand.

Using "without":

• Without your help, I can't finish this task.

• Option 1: "I can't finish this task unless you give me a hand."
• Option 2: "If you don't give me a hand, I won't be able to finish this task."
• Option 3: "I need your help to finish this task."