in a container hard water filled up to a height h a hole is made in the bottom the velocity of water flowing out of the hole is

if you remember that velocity of efflux is sqrt(2gh)

so basically if we will find the height of the water level then we can find velocity of efflux

as we know atmospheric pressure is 1atm and it is given that at bottom pressure is 3atm it means 2atm pressure is exerted by the water of the tank so just equate this pressure to

p=density*10*h

and find h, then put the value of h in formula of velocity of efflux you will get your answer