uh...

1. 4x + 8  = 4(x + 2)

2. -45 - 5x   =  -5 (9 + x)

3. 7x - 21   = 7 (x - 3)

oh... that's it?

xD

It is the opposite of expanding brackets.

4(x+2)=4x+8 and vice versa.

You have to find the highest common factor of the terms.

4x+8 = 4(x+2) (both terms can be divided by 4) 

-45 - 5x = -5(9 + x)

7x - 21 = 7(x + 3)

thx