So, the domain of this function is x is greater than or equal to 2 and is less than or equal to 6. So to find the range all you have to do is plug the lowest and highest values that x can be into the function equation.
f (x) is the same as the y value on the graph.
So in this case, 2 is the lowest value x can be
f (x) = (2)(2) - 4
f (x) = 0 <-- this is the lowest value in your range
the highest value x can be is 6
f (x) = (2)(6) - 4
f (x) = 8
So now we found the lowest and highest values y can be.
0 is less than or equal to y which is less than or equal to 8. This corresponds to number 1.