Calculate the solubility of Kcl2 in mole per dm cube of water at 90 dgree celcius if 10grams of the solute will saturate 20grams of water

I assume mean KCl and not KCl2.

Note the correct spelling of celsius.
10g KCl/20g H2O converted to L of water (assuming density H2O is 1.00 g/L) is
10 g KCl x (1000/20) = 500 g KCl
Then mols = grams/molar mass =?