At the beginning of an environmental study, a forest covered an area of $1500k{m}^2$ Since then, this area has decreased by $5\mathrm{.}25\%$ each year. Let I be the number of vears since the start of the study. Let $v$ be the area that the forest covers in $k{m}^2.$ Write an exponential function showing the relationship between $y$ and $1.$