In order to find the year when the water level is 100 mm higher than in 1880, let's use the value of f(x) = 100 and then calculate the value of x:
[tex]\begin{gathered} f(x)=1.6x \\ 100=1.6x \\ x=\frac{100}{1.6} \\ x=62.5 \end{gathered}[/tex]
So after 63 years then water level is 100 mm, so the year is 1880 + 63 = 1943
