Correct sentence: With its long ladder and a big water tank, the fire engine helps put out fires.
You also typed "chcek" — the correct spelling is "check."
This sentence is already correct. The first part, "With its long ladder and a big water tank," tells us more about the fire engine. We put a comma after that part because it comes before the main idea: "the fire engine helps put out fires."
Simpler way for a 7-year-old: The fire engine helps put out fires. It has a long ladder and a big water tank.
Another correct single-sentence option: The fire engine helps put out fires with its long ladder and big water tank.
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