The number of text messages, y (in billions), sent in the United States since 2005 can be
modeled using the equation y=18.8(3), where x is the number of years after 2005. In what
year were there approximately 4.6 trillion text messages sent?
A.2007
B.2008
C.2009
D.2010

How do you use the elimination method for this question? explain, because i really want to understand!

How many real-number solutions does the equation have? -4x^2 + 10x + 6 = 0 a. no solutions b. two solutions c. infinitely many solutions d. one solution

Max recorded the heights of 500 male humans. he found that the heights were normally distributed around a mean of 177 centimeters. which statements about max’s data must be true? a) the median of max’s data is 250 b) more than half of the data points max recorded were 177 centimeters. c) a data point chosen at random is as likely to be above the mean as it is to be below the mean. d) every height within three standard deviations of the mean is equally likely to be chosen if a data point is selected at random.