gmn cara mengerjakannya tlong donk

1. L= (a+b) × t : 2
= (5cm+7cm) × 3cm : 2
= 12cm × 3cm : 2
= 36cm2 : 2
= 18cm2

2. L= (a+b) × t : 2
= (12cm+8cm) × 4cm : 2
= 20cm × 4cm : 2
= 80cm2 : 2
= 40cm2

3. L= (a+b) × t : 2
= (4dm+2dm) × 3dm : 2
= 6dm × 3dm : 2
= 18dm2 : 2
= 9dm2

Itu jawabannya, maaf kalau salah:)