(a)
Every time we want to convert from one unit to another, we can think of it as part of the equation.
So, we have 16 years and want to convert to seconds. We don't have information to convert directly, but we can convert first to days.
So, we have 16 years, or 16 yr.
[tex]16yr[/tex]We want to cancel yr, and we know that:
[tex]\begin{gathered} 365days=1yr \\ \frac{365days}{1yr}=1 \end{gathered}[/tex]So, we can do the following:
[tex]16yr=16yr\cdot\frac{365days}{1yr}=16\cdot365days=5840days[/tex]Now we repeat for hours:
[tex]\begin{gathered} 24hrs=1day \\ \frac{24hrs}{1day}=1 \end{gathered}[/tex]So:
[tex]5840days=5840days\cdot\frac{24hrs}{1day}=5840\cdot24hrs=140160hrs[/tex]Now we repeat for minutes:
[tex]\begin{gathered} 60min=1hr \\ \frac{60min}{1hr}=1 \end{gathered}[/tex][tex]140160hrs=140160hrs\cdot\frac{60min}{1hr}=140160\cdot60min=8409600min[/tex]And finally to seconds:
[tex]\begin{gathered} 60sec=1min \\ \frac{60sec}{1min}=1 \end{gathered}[/tex][tex]8409600min\cdot\frac{60sec}{1min}=8409600\cdot60sec=504576000sec[/tex]So, there are 504576000 seconds in 16 years.