Answer-
The graph will be continuous because the amount of gas that she added to the tank does not need to be an integer amount.
Solution-
A graph of the function will be discrete, if the value of that function is always an integer. Otherwise, it will be a continuous graph.
In this case the graph will be continuous because the amount of gas that she added to the tank does not need to be an integer amount.
And since we can get, for example, 5.4, 6.9, etc gallons of gas, we can get amounts that are not integers.
y = total amount of gasoline in the tank
x = number of gallons that she added in the tank.
y = x + 4 (as 4 gallons of gas already in the tank)
And it is a polynomial function and all polynomial functions are continuous everywhere.