Given:
y' = –11 + 5x1 + 21x2 + 11x3 + 3x4
y' = –11 + 5x1 + 21x2 + 11x3 + 3x4 (we are to focus on the x1 term)
y' = –11 + 5(x1) + 21x2 + 11x3 + 3x4 (let's surround the x1 in parenthesis)
y' = –11 + 5(x1+2) + 21x2 + 11x3 + 3x4 ( let's replace x1 by x1+2 to indicate a change by 2)
y' = –11 + 5(x1+2) + 21x2 + 11x3 + 3x4
y' = –11 + 5x1 + 5*2 + 21x2 + 11x3 + 3x4
y' = –11 + 5x1 + 21x2 + 11x3 + 3x4 + 5*2
y' = –11 + 5x1 + 21x2 + 11x3 + 3x4 + 10
y' = –11 + 5x1 + 21x2 + 11x3 + 3x4 + 5*2
We can see that we have gotten a new y' value from what we did above.
Note how we simply add 10 to the old y' value to get the new y' value.
Therefore, y' is changing by 10 when x1 changes by 2
So, the correct option is the first option which is 10.