So we have the area of the biggest/top part: 180cm^2
For the bottom part:
You've said the length of the bottom side is 8cm.
We know the length of the biggest side: 24cm. And we know the length of the opposite side: 18cm. So, to find the length of the missing side, it's simple subtraction:
24cm - 18cm = 6cm
So now we have lengths for 2 sides: 8cm and 6cm.
Multiply these to give the area:
8cm * 6cm = 48cm^2
Add these areas of both shapes together to give total area:
