we are given
Volume of water in lake in mi^3
[tex]V=2900mi^3[/tex]
now, we know that
[tex]1 mi^3= 1.10111715*10^{12} gallons [/tex]
we can multiply both sides by 2900
[tex]2900*1 mi^3= 2900*1.10111715*10^{12} gallons [/tex]
[tex]2900*1 mi^3= 3193.239735*10^{12} gallons [/tex]
we can write in scientific form
[tex]2900 mi^3= 3.193239735*10^{15} gallons [/tex]...........Answer
