Find the amount of water at 20°c required to just melt 5g of ice at -20°c

At -20c ice absorb 50 cal and at 20c water released 20x if we consider mass as x. so at 0c ice should absorb 20x-50 cal. So 20x-50 =Mmelt×80 so mmelt is 20x-50/80 and we require total mass of ice should be melt so 20x-50/80=5 we get x=22.5