From 1989 to 1990, the population of Nevada

increased by 1.59 × 105, and that of Maine
increased by 28000. In 1990, the population
of Nevada was 1206152, and that of Maine was 1233223.
If the populations of the two states continue
to increase at the same rates, in what year will
the population of Nevada and Maine be the
same?

This is not geometry. It is algebra

Write two equations for population vs time (measured in years after 1990)) and set them equal. Then you can solve for the time.