Assuming you are supposed to write each conversion in scientific notation:
(2) 1 m = 100 cm, so
(67 cm) × (1/100 m/cm) = 67/100 m = 0.67 m = 6.7 × 10 ⁻¹ m
(3) 1 km = 1,000 m, so
(1.2 km) × (1000 m/km) = 1200 m = 1.2 × 10³ m
(4) 1 m = 1,000 mm = 10³ mm, so
(6.2 × 10 ⁻³ m) × (10³ mm/m) = 6.2 mm
(5) 1 m = 1,000,000,000 nm = 10⁹ nm, so
(4.05 × 10³ nm) × (1/10⁹ m/nm) = 4.05 × 10 ⁻⁶ m
(6) 1 g = 1,000,000 µg = 10⁶ µg, so
(3200 µg) × (1/10⁶ g/µg) = 3200 × 10 ⁻⁶ g = 3.2 × 10 ⁻³ g
