Answer:
12 cups of salad in total.
Explanation:
First we have to set a letter to represent the number of cups added, this will be X, and we have to represesent the values like this:
Cups of spinach in inital salad blend: 4(.4)
Cups of spinachs in added salad blend: .55(x)
Total amount of cups of spinach: .50(x+4)
So we know that if we add the inital to the added cups we get the total, so that´s our equation:

By clearing X we get that the number of cups added is 8, if we originally had 4, we now that the resultant salad will hace 12 cups of mixture.