Nominal GDP = $15 Trillion
Real GDP = $3 Trillion
M = $600 Billion
Having them in billion units,
Nominal GDP = $15000 Billions = P x Y
Real GDP = $3000 Billions = Y
P = P x Y/ Y = 15000/3000 = 5
As we know M x V = P x Y which gives V = (P x Y)/M = 15000/600 = 25.