Why does the mediterranean sea and red sea have more slat then the baltic sea

Because both seas are close to Africa, where salt is mostly from, the salt in the ground goes to the seas and is in the water, cosequently makes it more salty than the other.

There are parts of the ocean where little rain falls but warm dry winds cause lots of evaporation. This evaporation removes water and when water vapor rises into the atmosphere, it leaves the salt behind, so the salinity of the seawater increases. One of these places is the Mediterranean sea. The Baltic sea doesn't have this condition and also has multiple rivers flowing into it so it's water is less salty.