The sum of 9 and three times a number is 21. what is the number?
equation:

n =

Suppose i flip two identical coins. what is the probability that i get one head and one tail?

Ben is three times as old as samantha, who is two years older than half of michel's age. if michel is 12. how old is ben?

The swimming pool is open when the high temperature is higher than 20∘c. lainey tried to swim on monday and thursday (which was 3 days later). the pool was open on monday, but it was closed on thursday. the high temperature was 30∘c on monday, but decreased at a constant rate in the next 3 days. write an inequality to determine the rate of temperature decrease in degrees celsius per day, d, from monday to thursday.