Fast i really don't understad this i need its so frustrating

Select all the correct answers. what is 221,000,000,000,000,000,000 expressed in scientific notation?

Use the frequency distribution, which shows the number of american voters (in millions) according to age, to find the probability that a voter chosen at random is in the 18 to 20 years old age range. ages frequency 18 to 20 5.9 21 to 24 7.7 25 to 34 20.4 35 to 44 25.1 45 to 64 54.4 65 and over 27.7 the probability that a voter chosen at random is in the 18 to 20 years old age range is nothing. (round to three decimal places as needed.)

Which equation results from adding the equations in this system? x+6y=9 and -x+2y=-15