Let's look at some examples:

To get from odd integer 3 to the next odd integer 5 you have to add 2.  
To get from odd integer 5 to the next odd integer 7 you have to add 2.
To get from odd integer 7 to the next odd integer 9 you have to add 2.
To get from odd integer 9 to the next odd integer 11 you have to add 2.

So every time we had to add 2 to an odd integer to get to the next odd
integer.

Therefore we reason this way: if 5x is an odd integer, then
to get to the next odd integer we must also have to add 2 to it like the
odd numbers above.

To add 2 to 5x we stick "+ 2" beside it and leave it that way:

Answer:

            5x + 2

That really wasn't very hard, now was it?

Edwin