Brainiest goes to the first correct answer thanks

20

Step-by-step explanation:

we can see that there are already answers for 2 which is six 6+6=12 now we can see that a triangle look the same as the six over the 8mm so that must be six so 6+6+6=18 now there is still s little section missing over the 8mm (the half triangle half square) is missing a section we can see that the perimeter is 8 and the area is 6 and 6+2=8 so that little area is 2 so 6+6+6+2=20