Suppose you dissolve 12.8 g of one substance in 11 g of another. is this reasonable? explain

No, its not reasonable.

Explanation:

The substance that is to be dissolved is known as solute. The substance that is dissolving is known as solvent.

The amount of solvent  in the mixture should be greater than that of solute.

Suppose we are taking a solvent in a beaker and we are continuously adding solute in it. Initially the solute dissolve quickly. At some point the solute stops dissolving in the solvent. This is known as saturation point of the solvent. After saturation point if solute is added further it does not dissolve in the solvent.

So, its not possible to dissolve 12.8 g of one substance in 11 g of another.

they should be similar or the same