Study the sample grids and build them.

The sample shows a main square with numbers at the top (T), right (R), left (L), and a number in a small box attached to the left side (OL). The result (X) is in a small box attached to the top-left corner.
For the sample, we have: T=4, R=1, L=3, OL=2, and X=15.
Let's test the pattern: $X = |T - R| \times (L + OL)$.

This pattern matches the sample. The numbers at the bottom and center of the main square are not used in this pattern.

For the first problem below the samples, we have:
Top (T) = 4
Right (R) = 1
Left (L) = 3
Outside Left (OL) = 'e'

By carefully observing the character 'e' in the problems, it consistently appears to be the digit '3'. For example, the 'e' in the outside left box of the first problem looks like a '3'.
Therefore, we assume 'e' = 3.

Using T=4, R=1, L=3, and OL=3 (since 'e'=3):

The missing number is 18.

The final answer is 18.