Chapter 6 - Section 6.6 - Logarithmic and Exponential Equations - 6.6 Assess Your Understanding - Page 467: 105

See below.

a) Our equation is: $400=317\cdot1.007^{t-2014}\\\frac{400}{317}=1.007^{t-2014}\\\log_{1.007}{\frac{400}{317}}=t-2014\\t=\log_{1.007}{\frac{400}{317}}+2014\approx2047.34$ b) Our equation is: $435=317\cdot1.007^{t-2014}\\\frac{435}{317}=1.007^{t-2014}\\\log_{1.007}{\frac{435}{317}}=t-2014\\t=\log_{1.007}{\frac{435}{317}}+2014\approx2059.36$