It would be 12
I don’t have any paper but I’ll try and explain
So to factorize you need two numbers that multiply to 20
In the form ax^2+bx+c=0
So 10 and 2
You can see that the sum of 10 and 2 is 12
If you were to factorize this you would get
x(x+2)+10(x+1)
(x+2)(x+10)