total active iPhones in US in millions of units total active iPhones in US in millions of units vs. year -7.17+-11.8x+2.12x^2+-0.0578x^3 ear 8 8 9 17 10 24 11 40 12 51 13 72 14 88 15 101 16 114 17 125 18 127 19 131 20 138 21 141 22 149 total active iPhones in US in millions of units 150 100 50 0 8 10 12 122 14 year 16 18 20 22 22