What are the sums of the following addition problems: 0+4, 9+0, 0+4, 0+5, 0+6, 0+1, 2+0, 0+3, 8+0?

For $0 + 4$:

$$0 + 4 = 4$$

The sum is $\boxed{\text{4}}$.
For $9 + 0$:

$$9 + 0 = 9$$

The sum is $\boxed{\text{9}}$.
For $0 + 4$:

$$0 + 4 = 4$$

The sum is $\boxed{\text{4}}$.

For $0 + 5$:

$$0 + 5 = 5$$

The sum is $\boxed{\text{5}}$.
For $0 + 6$:

$$0 + 6 = 6$$

The sum is $\boxed{\text{6}}$.
For $0 + 1$:

$$0 + 1 = 1$$

The sum is $\boxed{\text{1}}$.

For $2 + 0$:

$$2 + 0 = 2$$

The sum is $\boxed{\text{2}}$.
For $0 + 3$:

$$0 + 3 = 3$$

The sum is $\boxed{\text{3}}$.
For $8 + 0$:

$$8 + 0 = 8$$

The sum is $\boxed{\text{8}}$.