A Ferris wheel rotates at a constant speed. The wheel's radius is 18 feet and the bottom of the wheel is 6 feet above ground level. From a point in front of the wheel Christina is watching a pink ribbon tied to a friend’s hair. The wheel takes 18 minutes to complete one revolution. She first notices the ribbon when her friend gets to the top of the Ferris wheel. What is the period?

First step is to get rid of the square root. remember that a square root is the same as raising to the (1/2) power. see below: multiply exponents per exponent rules to get: remember you subtract exponents from the denominator and add exponents in the numerator so: simplify further: so a is the correct choice. if you don't understand this google exponent rules and it will you understand. look at the image results.