Tim owns shares in a mutual fund. His investment was worth $4,200 when he first bought the shares. One year later, his shares were worth $4,410.

Let t represent the number of years since Tim first bought the shares. Assuming the value has increased exponentially, which expression best models the value of Tim's shares over time?

The expression that best models the value of Tim's shares over time is $4200 \times (1 + r)^t$, where $r$ represents the growth rate per year.