Just like you drew those dotted lines. You know how to find the areas of rectangles which is A=length x width
The answer would be 20cm^2+6cm^2+18cm^2=44 cm^2
You would divide it into smaller shapes and then find the area then add them all up.
4*5=20
3*2=6
3*6=18
20+6+18=34cm^2
