So im going to factor each expressions
15k + 9 are both divisible by 3 so it is the same as
3(5k+3) (distribute the 3 and you get your original equation)
3(2k+3) +9k
6k+9+9k
15K+9 and do the same thing above
Since each input has one and only one output, f(x) is TRUE
The 69.15 percentile corresponds to 0.500 standard deviations above the mean. If 70 is 10*.500 = 5 units above the mean, then the mean is 65.