VA is the stalling speed at the limiting load factor. So this question concerns the way in which stalling speed changes with changes in weight.
The general solution for finding the change of stalling speed for any given change in weight is,
Vs at new wt = Vs at old wt x sguare root (new wt/old wt)
As Dick said, for small weight changes the % change in Vs is about half the % change in weight.
Even for a 50% increase in weight this approximation gives 25% increase whereas the actual figure is 22.47%, so it is still reasonably close.