Here are the answers

1. 4.5 x 10^-12
2. 3.1 x 10¹²
3. 4.0 x 10⁶
4. 4.3 x 10¹⁸
5. 9.8 x 10¹⁹ - you'll notice this one is the same as the first number in the problem, that's because the numbers are so different (one really large, the other small), that adding them makes no difference to the value of the large value.