This is an exponential growth problem. Exponential growth can be expressed mathematically in the following way:
![y=a (1+r)^(t)](https://img.qammunity.org/2019/formulas/mathematics/high-school/hv3jqkn5enkstowsq6g7m9oy1eqn06y3u6.png)
.
Parameter a presents initial amount.
Parameter r is percentage increase.
Parameter t is time.
An equation that would describe given problem is:
![y=400 (1+0.02)^(t)](https://img.qammunity.org/2019/formulas/mathematics/high-school/6oufw4rwmh68on77p775up8feowqa9orui.png)
t is the time in years.
I attached the graph of this function.