Area = base × height = 12 cm × 4 cm = 48 cm².

Area = 1/2 × base × height = 1/2 × 10 cm × 6 cm = 30 cm².

Perimeter = 2(length + width), so 30 cm = 2(10 cm + width). Width = (30 cm/2) - 10 cm = 5 cm.

New area = (2 * length) * (width/2) = length * width = original area, so it doubles.

Area = (3√3/2) * side² = (3√3/2) * 4² = 24√3 cm².

Area = side² = 9 cm × 9 cm = 81 cm².

Area = 1/2 × (base1 + base2) × height = 1/2 × (10 cm + 6 cm) × 5 cm = 40 cm².