Which graph and function models this situation?

Consider the following. 

graphs are made of coordinates, Coordinates are made of x and y values 

x values are typically the input while y values are the output 

Basically 
The x values are the time (input) and the y values are the cost (output) 

Thus
The answer would be graph D

Becuase 
For the first set of records 
It would be up to 60 minutes (which is either 1 hr or less than one hr) for 5$
Less than or equal to 1 is 5$
So yeah D 

For a 0.25 pfor b o.3pp (0.25+0.3)=0.28

Ithink it is b and d