Step-by-step explanation:

1)we have to add 7b +2b-4b

taking b as common

we get b(7+2-4)=5b

2)3xy+3-4xy+2+9xy+4

=3xy-4xy+9xy+3+2+4

taking xy as common xy(3-4+9)+9

=8xy+9.

3) similarly you can do for 3rd one.

3a-3b-3b+4+a-b-2

=4a-7b+2

Step-by-step explanation:

1) 7b+2b-4b

= 9b-4b

= 5b

Ans:- 5b

2) 3xy+3-4xy+2+9xy+4

3xy + 3

- 4xy + 2

9xy + 4

____________

8xy + 9

____________

Ans:- 8xy+9

3) 3a-3b-3b+4+a-b-2

3a - 3b

- 3b+4

a - b - 2

_____________

4a -7b +2

_____________

Ans:- 4a-7b+2