What’s number #8 help me please

Which values for a and b will create infinitely many solutions for this system of equations? ax-y=8 2x+y=b

Which of the following is a proper fraction? a. 9⁄8 b. 5⁄6 c. 7⁄3 d. 4⁄2

In one day there are too high tides into low tides and equally spaced intervals the high tide is observed to be 6 feet above the average sea level after six hours passed a low tide occurs at 6 feet below the average sea level in this task you will model this occurrence using a trigonometric function by using x as a measurement of time assume the first high tide occurs at x=0. a. what are the independent and dependent variables? b. determine these key features of the function that models the tide: 1.amplitude 2.period 3.frequency 4.midline 5.vertical shift 6.phase shift c. create a trigonometric function that models the ocean tide for a period of 12 hours. d. what is the height of the tide after 93 hours?