The first expression is
[tex]2x+3.2x-1[/tex]We have to reduce like terms
[tex](2+3.2-1)x=4.2x[/tex]The first answer is 4.2x
The second expression is
[tex]3a+4b+2a-9b=3a+2a+4b-9b=5a-5b=5(a-b)[/tex]The third expression is
[tex]3a+5ab=a(3+5b)[/tex]Observe that in the third expression we only factored out the greatest common factor which was a.