As y varies directly as x, we have a linear relation for x and y that goes through the origin (the point (0, 0) belongs to the line).
Other point that belongs to the linear relation is (x=15; y=48).
We have the relation:
b=0, as y varies directly as x.
Using the point (15, 48) we have:
Then, the equation that relates y to x is:
When y=16, this corresponds to an x value of:
When y=16, x=5.