Afull lake begins dropping at a constant rate. after 4 weeks it has dropped 3 feet. what is the unit rate of change in the lake's level compared to it's full level ?

A full lake is dropping at its constant rate, meaning it is unchanging over time.
After 4 weeks’ time, it already dropped 3 feet.
Now, let’s solve for the Unit rate based on the given data.
=> 3 feet in 4 weeks
=> Unit rate is 3 feet per 4 weeks
=> in 4 weeks there are (7 * 4) = 28 days
=> 3 feet / 28 days  
=> the Unit rate is .107 feet / day

Need the graph to answer this.