Final answer:
Sofia made a mistake in step 3 of finding the inverse of function f. In this step, Sofia should have replaced y with x.
Step-by-step explanation:
Sofia made a mistake in step 3 of finding the inverse of function f. In this step, Sofia should have replaced y with x. This step is essential in finding the inverse of a function by switching the x and y variables. By doing so, the unknown variable in the original function becomes the dependent variable in the inverse function.