Formal or informal language

Is the following sentence an example of formal or informal writing?

I didn't need any help.

Is the following sentence an example of formal or informal writing?

Let's watch some TV this weekend.

Is the following sentence and example of formal or informal writing?

We found out when they met up.

Is the following sentence an example of formal or informal writing?

Many children in the world lack adequate food and housing.

Is the following sentence an example of formal or informal writing?

I've been under the weather lately.

Is the following sentence an example of formal or informal writing?

I would like to apologise for any inconvenience I may have caused.

Is the following sentence an example of formal or informal writing?

Furthermore, we have seen the number of units sold increase dramatically.

Is the sentence an example of formal or informal writing?

Lots of students have dropped their course this term.

Is the following sentence an example of formal or informal writing?

Write back ASAP.

Is the following sentence an example of formal or informal writing?

To top it all off, I have to work on Monday.