Can you please go step by step, Ill show what I did and you can correct me.

The question is:
a+a(x+1)

My way:

a+a(x+1)
2a(x+1)
2ax+2a

Could someone please check over this and provide a correct answer and my error.

Thanks in advance.

a+a(x+1) does not equal 2a(x+1)

If it was (a+a)(x+1), then that would work, but it's not.

The correct next step is:
a+a(x+1)=a+ax+a

Thank-you

You may not add the terms a and a(x+1) since they are not the same. You can add a and a or a(x+1) and a(x+1) but not the in-between.
Firt, expand the second term by multiplying each term withing the parentheses by a.
a+a(x+1)=
a + ax + a =
then you may add the same terms to obtain:
2a + ax =
I don't know where you are going with this equation or the final form in which it is to be found; however, you can now factor out a to obtain
a(2+x). That is how I would leave it.