Let's denote the total amount Dylan received for all 4 DVDs as \( x \). According to the problem, after Dylan bought the backpack for $16.40, he had $3.60 left. Therefore, we can set up the following equation:
\[ x - 16.40 = 3.60 \]
Now, we solve for \( x \):
\[ x = 16.40 + 3.60 \] \[ x = 20.00 \]
Dylan received a total of $20.00 for all 4 DVDs. To find out how much he received for each DVD, we divide the total amount by the number of DVDs:
\[ \text{Amount per DVD} = \frac{20.00}{4} = 5.00 \]
Therefore, Dylan received $5.00 for each DVD in the set.