Grammar – Purpose of ‘By’ in ‘Stop Back By’: Usage Explained

In both sentences the predicate should be "is". The rules are the following: if the subject is expressed by either of, none of, neither of we use a singular verb as we mean one item ( "either of" meaning "either this or that one"), in the second sentence we have "as well as", the sentence can be rephrased: working out just like reading ( we compare two things, but caracterise one of them, the first one, so the predicate agrees with it, if it' s singular the verb is singular and if plural it requires a plural verb

Normally you would say:

I will come back to you later.

if you are staying on the connection (internet or phone).

If you will drop the connection to resume later on, then:

I will get back to you later.

This also works in personal communication. Let's say you ask your professor something, but he needs to speak to another student first. He might say to you:

I will come back to you later.

When he does, let's say he needs to do some research back at his office before he can answer. In that case:

I will get back to you later.

Some people might use "later on", but it is unnecessary.