I've been having trouble with my car's digital fuel marker and the needle, which are two different systems to check and know when fuel needs to be added. The problem is that they do not correspond to one another, for example: the needle says 1/4 tank is full and the digital marker (which supposedly informs how much fuel is left in term of miles) says 30 miles. After adding some fuel to the car, the needle reacher 1/2 of the tank and the marker only raised 5 miles. Something is wrong with my car and I don't know what.

My speedometer isn't working any suggestions