The answer to the question is rational.
You can choose a couple of the x-values and plug each into all of the x's in each equation on the right. Then see which equations give the y-values equal to the y's adjacent to the 3 x-values you used. I chose x=-4 and x=8. Only the 2nd, 3rd, and 5th equations matched with both.
Let's check the dot product .
v.w = 5(4)-2(10) = 20 -20 =0
So the dot product is not 20 . And since the dot product is zero, so they are perpendicular.
And the y component of w is 10.
So correct options are first and third .
$21 because 3$x$7(numbers of days in a week)is $21. I hope this helps :)