Hey!

The solution is as follows :

Solubility of potassium nitrate at  313K = 62/100

100 g of water contains potassium nitrate = 62 g

50 g of water contains potassium nitrate = 62/100 X 50 = 31g

Thus, 31 g potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 g of water at 313 K.

Hope it helped to clear your delimma

Thank you