Excel Text

I have a column that contains the Full Name, such as Matthew Groff. I want to change the Full Name column to read Groff, Matthew

I wrote the formula =MID(B8,FIND(" ",B8)+1,100)&”,”      and this gives me Groff,

I wrote the formula =LEFT(B8,FIND(" ",B8)-1)            and this gives me Matthew

I tried to combine them with =MID(B8,FIND(" ",B8)+1,100)&”,”&LEFT(B8,FIND(" ",B8)-1)

But this gives me a Name error that I can't figure out. I have attached my sample file.