How do you subtract 7x 3 - 5x 4?

To subtract 7x^3 - 5x^4, you first need to rearrange the terms in descending order of the exponents. So, the expression becomes -5x^4 - 7x^3. Since the terms have different exponents, you cannot directly subtract them. The result is simply -5x^4 - 7x^3.