The saltier mixture will have more teaspoons of salt per cups of water.
For mixure B, we have 2.5 cups of water per teaspoons of salt this is 1/2.5 = 0.4 teaspoons of salt per cups of water.
Now, we need to calculate the relation between teaspoons of salt per cups of water for mixture A, so:

So, mixture A has the greater relation of teaspoons of salt per cups of water, so it's saltier than mixture B.