18/
5×4=20 mere...............
19/
|----|----|----|----|----|
|----|----|prima zi
|--------------|rest
|-|-|-|-|-|-|-|-|-|a doua zi
|-|-|-|-|-|a doua zi
|------|
|-|-|-|-|
|-|a patra zi
|-----|12
12:3=4
4x4=16
16:4=4
4x9=36
36:3=12
12x5=60