In a parallelogram, opposite sides are equal in length. Thus, for quadrilateral JKLM, we can set up the following equations based on the side lengths given:
- \( JK = LM \) which implies \( 16 = x + 15 \)
- \( KL = JM \) which implies \( 13 = 13 \) (this is already equal)
Now, let's solve the first equation for \( x \):
\[ 16 = x + 15 \]
Subtracting 15 from both sides gives:
\[ 16 - 15 = x \] \[ x = 1 \]
Therefore, the value of \( x \) must be \( 1 \).