Using this calculator you can simulate which level of earnings you will have depending on your downloads. Shutterstock determines your royalties level based on the number of downloads in a given year.
You can see the blue line which represents number of downloads in your account through each month of the year (left axis). Also you can see the red line which represents your royalties level (right axis).
Shutterstock pays you royalties based on customer subscriptions so it's quite hard to estimate what amount of dollars you will earn having this royalties rate.