Use of "results" in "Substituting for the numbers results in equation A" correct?

Question

I have the following sentence:

From Equation 1, x=1 and y=2. Since z=x+y, substituting for the numbers results in z=3.

I want to just check the usage of "results" is correct. My logic is that substituting for the numbers is a singular "act", as in the act of substituting for the numbers results in equation A.

Am I correct?

MS word has failed to enlighten me, accepting both versions without highlighting :)

In addition, the following doesn't sound right:

The static nonlinearity was modelled by firstly simple polynomial and then dual-polynomial functions, the latter of which reduces the number of parameters required and the accuracy of the model.

At first glance, I should probably change reduces to reduce, as the functions are plural. But something is telling me the `latter of which' is needlessly complicated, so I attempt to write it as:

The static nonlinearity was modelled by firstly simple polynomial and then dual-polynomial functions, with the latter reducing the number of parameters required and the accuracy of the model.

Please advise on both the validity of the change.

EDIT: Altered original example and added 2nd part

Answer 1

The first sentence would flow better as

... substitution results in z=3."

but "results" is, indeed, correct.

For your second example, unless you're referring to "firstly simple" polynomials, that part should read

"... modeled firstly by simple polynomials..."

Second, either hyphenate both types of polynomials or neither. The rest of your change is valid.