<h2>
Answer:</h2>
The correct graph is attached to the answer.
The amount of fruit syrup Rex added is: 3 liters
and the amount of water he added is: 4 liters.
<h2>
Step-by-step explanation:</h2>
x denote the amount of fruit syrup added and y denote the amount of water added.
It is given that:
Three times the number of liters of water he mixed was 6 more than twice the number of liters of syrup he mixed.
i.e. the equation that satisfies this condition is:

i.e. the graph of this equation is a line that passes through (-3,0) and (0,2)
Also, The total number of liters of syrup and water he mixed was 7 liters.
Hence, the equation is:

i.e. the graph of this equality is a line that passes through (7,0) and (0,7)
Also, from equation (2) we have:

Now, on putting this value of x in terms of y in equation (1) we get:

Also, on putting the value of y in equation (2) we get:

Hence, the solution to the system of linear equation is:
(3,4)