Vs is proportional to Vmd.

 

Vmd is proportional to the square root of weight or load factor change

 

load factor change = 5000/6850 = 0.729

 

square root of 0.729=0.85

 

Original Vs = 78KCAS

 

New Vs= 78 x 0.85 = 67KCAS.