Factoring help?

a³x²m² + a²xm³ - a⁴x³m²
= a²xm²•ax + a²xm²•m + a²xm²•a²x²
= a²xm²(ax + m + a²x²)

a³x²m² + a²xm³ - a⁴x³m²

To factor out the greatest common factor, look for the lowest exponent from the set of factors.  If a term doesn't have a factor, treat that exponent as a 0 (since anything to the 0 power is 1).  Since all three terms have all three variables, the GCF has the smallest exponents from the three terms.  In this case, it is:

a²xm²

Then divide each term by this GCF to get the remaining trinomial as the second factor:

a²xm²(ax + m - a²x²)

That's all it's asking you to do.

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Side note, finding the least common multiple is exactly the same except you use the largest exponent from each factor:

a⁴x³m³

  Factor out the Greatest Common Factor: 
  a^3x^2m^2 + a^2xm^3 - a^4x^3m^2
  = a^2xm^2(ax + mx - a^2x)