Chapter 12 - Section 12.8 - Exponential and Logarithmic Equations and Problem Solving - Exercise Set - Page 898: 55

16.1 years

$y=y_0*e^{-0.003t}$ $y_0=9970000$ $y=9500000$ $y=y_0*e^{-0.003t}$ $9500000=9970000*e^{-0.003t}$ $9500000/9970000=9970000*e^{-0.003t}/9970000$ $950/997=e^{-0.003t}$ $.952859=e^{-0.003t}$ $ln {.952859} = ln e^{-0.003t}$ $ln {.952859} = -0.003t$ $-.048288 = -.003t$ $-.048288/-.003 = -.003t/-.003$ $16.096 = t$