Well, let's take a moment to appreciate these lovely variables, f and g. To simplify this expression, we can combine like terms. So, when we combine the terms with f, we get 5f - 7f + 3f, which simplifies to f. And when we combine the terms with g, we get -3g - 4g, which simplifies to -7g. So, the simplified expression is f - 7g. Remember, there are no mistakes in math, just happy little accidents.