Subtract the area of △ABE and △BCH from the area of the whole rectangle.

Then you'll notice that you subtracted one extra area, which is BFGI.

So add it back.

Could u write it down? I don't really quite understand

Thx

AC = AB + BC = 12cm + 6cm = 18cm

Area of rectangle ACDJ = AC × CD
= 18cm × 7.2cm
= 129.6cm²

Area of △ABE = ½ × base × height
= ½ × 12cm × 7.2cm
= 43.2cm²

Area of △BCH = ½ × base × height
= ½ × 6cm × 7.2cm
= 21.6cm²


Shaded area = area ACDJ - area ABE - area BCH + area BFGI

= 129.6cm² - 43.2cm² - 21.6cm² + 21cm
= 85.8cm²