The exponent rule needed here is that, if the bases are the same (they're all m), you add the exponents when multiplying the terms. I believe it's called the exponent product rule (?) Here, this means you're adding the powers of m: 2, 5, and -3, or 2 + 5 - 3, which is 4, so your answer is m^4. Let me know if you need a more thorough explanation.
