For all proportion problems, start with this:

Varying           "directly" or product of "jointlys" or 1 if none 
quantity  = k · ----------------------------------------------------------
                inversely variable or product of "inverselys" or 1 if none

In this problem the varying quantity is y.
there are no "directly"s or "jointlys", so we have 1 on top.
We have one inversely, x.  So we have x on the bottom:

y = k·

>>...y=5 when x=14...<<

Substitute these values:

5 = k*

Multiply both sides by 14

14·5 = k

70 = k

Edwin