Answer:

Explanation:
9 x 9 x 9 x 9 is 9 multiplied by itself four times, so it's 9 to the 4th power as typed above.
D.
Although letters may be informal as well, commercials tend to be the most informal.
After the first use of 'astronaut'
Answer:
I don't get this problem,please give me more information so I can help you.
Explanation: