Question

How do you write word phrases for these expressions: `3+a`?

Answer 1

An expression something like:
The sum of 3 and a number.

Explanation:

In algebra we refer to a variable as "a number"

The operation "+" can be said as any of the following:

"the sum of"
"added to"
"increased by"
"more than"

So, to express `3+a` in words, could be:

The sum of 3 and a number.
A number added to 3.
3 increased by a certain number
3 more than a number