How do i tell sales tax of 2.50 how much is the total

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.)

If f(x)=3x+1 and f^-1=x-1/3, then f^-1(7)=

Nine more than four times a number is the same as one less than twice the number. find the number?