+1Twice as much salt but twice as much volume too, so the salinity does not change.
See here: https://sciencing.com/calculate-mix-chemical-solutions-8706412.html
“Calculate appropriate v/v dilution using the formula C1V1 = C2V2 where C represents the concentration of the solute, and V represents volume in milliliters or ml. An example would be combining 95 percent ethanol with water to mix 100 ml of 70 percent ethanol. The calculation is 95% X V1 = 70% X 100ml”