How do you turn (g solute/100g H2O) to percent mass

I don't know what the formula is or how to convert, I know it's probably really simple, but I don't want to get it wrong.

Please help! Thanks!

easiets way is to assume a mass. since this is based on 100g H2O.. let's assume we have..100g H2O

and..
100g H2O x (X g solute / 100g H2O) = Xg solute

so..
total mass = X + 100

mass % = X / (X + 100) x 100%