In the first case, just multiply both values. In the second case, you must also multiply the number by itself, but to do so carefully move the comma.
1. 4.5x30 g
2. 1.99x10-8 cm
1) 4.5 * 30 = 135g = 0.135 kg (if you want to in kg)
2) 1,99*0.00000001 = 0.0000000199 cm