Answer:
2(x + 21y)
Explanation:
Factorising is the reverse of expanding brackets, so you need to turn the equation into something that can be expanded.
In order to do this, you must find a common factor of your two values, which in this case is 2.
You put this common factor on the outside of your brackets, and then put on the inside your equation divided by that common factor - in this case 2.
This leaves us with our answer, 2(x + 21y)
You can check that this is right by multiplying everything on the inside of the brackets by 2. That will leave us with our original equation, 2x + 42y