We are told that y varies directly with x and are given that the following (x, y) point : (3, -39) represents that relationship.
So we notice that for x = 3, the related y is -39. so we can assume that there is a constant of proportionality (k) between these two numbers, such that :
y = k x
if y = -39 when x = 3, then the constant k must be -13:
-39 = (-13) (3)
then , applying this proportionality we can find what the x-value is in the incomlete pair: (x, 65):
y = -13 x
65 = -13 x
therefore x = 65/(-13) = - 65/13
and our completed pair is: (-65/13 , 65)
