How can the graph be used to predict the output (y-value) associated with the input of 3 1/2?

Rule: y = 2x + 1

Graph
Input: -6, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, 6
Output: -11, -9, -7, -5, -3, -1, 1, 3, 5, 7, 9, 11, 13

Question

How can the graph be used to predict the output (y-value) associated with the input of 3 1/2?

Rule: y = 2x + 1

Graph
Input: -6, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, 6
Output: -11, -9, -7, -5, -3, -1, 1, 3, 5, 7, 9, 11, 13

anonymous · Answer

you can substitute 3 1/2 for x in the equation from the rule
$$y=2\left( 3\frac{ 1 }{ 2 } \right)+1$$

anonymous · Answer

or you can look at the table. 
$3\frac{1}{2}$ is halfway between input-values 3 and 4. 
The corresponding output-value will be halfway between 7 and 9.