Question

4x +7y

Answer 1

(4x-7y)/9y-((5x+2y)/12y-1)
= (4x/9y - 7/9)-(5x/12y + 1/6 -1)
= (4x/9y - 5x/12y) + (-7/9 - 1/6 +1)
= x/36y + 1/18
= (x + 2y)/(36y)

Either of the last 2 lines of working would probably be ok

Answer 2

Are you sure that's the question, perhaps you skipped something in it?

Answer 3

What can I possible do with 4x+7y, nothing, or maybe, derive them? then \[(4x+7y)'=(4x)'+(7y)'=4+7=11\]