What is 8.1 times 10 to the tenth power?

What is the simplified form of (3.25x10^3)(7.8x10^6) written in scientific notation?

Mat bought a phone for $100. he has to pay $30 per mouth. if he has paid $640 in total, how many mouth has he had the phone?

Awoman has 14 different shirts: 10 white shirts and 4 red shirts. if she randomly chooses 2 shirts to take with her on vacation, then what is the probability that she will choose two white shirts? show your answer in fraction and percent, round to the nearest whole percent.