Final answer:
The expression 9g - 4f remains unchanged as x and y are not part of it, and no additional relationship has been provided to link g and f to x and y.
Step-by-step explanation:
The expression 9g - 4f does not contain the variables x or y, so even when given the values x = -6 and y= 5, they do not influence the simplification of this expression. Therefore, without additional context or information on the relationship between g, f, and the variables x and y, the expression remains 9g - 4f.