We can set up the following equation:
4x + 4(5) = 54
X representa the cost of a salad, and the 4(5) shows how each time she left a tip of 5.
Now we solve:
4x + 20 = 54
Subtract 20 from each side:
4x = 34
Now divide by 4
X = 8.5
So the cost of each salad is $8.50
I hope this Helps!