Hey there!!
We have:
... 4ax+3ay+4bx+3by
Now, let's group these terms.
... 4ax+4bx+3ay+3by
Now, we have grouped these terms. We have two sections.
4ax+4bx and 3ay+by
Now, let's take common term in both these sections.
... 4ax+4bx (The common term is 4x )
Hence, this would become:
... 4x(a+b)
And 3ay+by
(The common term,is 3y )
... 3y(a+b)
Hence, the equation would be :
... 4x(a+b)+3y(a+b)
... (4x+3y)(a+b)
Hence, the blanks are 'a', '4'and '3'
Hope my answer helps!