Given that a function
g(d) = 600-50d
Here g is dependent variable and d independent variable
We have to interpret the term 50 in this situation.
g = 600-50d
600 represents the initial amount of water in the tank i.e. when d =0
Let us assume d changes by 1 day. say d+1
then new g = g' = 600-50(d+1) = 550-50d
i.e. whenever d increases by 1 unit, g decreases by 50 galons
Hence correct answer is
The volume of the tank decreases by 50 gal every day.