INeed some help on my "Red Eared Slider Turtle" please.?

Hi, it sounds like your red eared slider is probably young if he is still 3-4 inches. But honestly there is no way to tell the turtles exact age unless you see them being born. Your tank water should cover his shell but he should also have an area to easily climb up on to bask in a reptile lamp. You should also have a heater and filter in your tank. If the water is too cold the turtle can get sick. As for the webbing on the back feet and not on the front feet, that is perfectly normal. All red eared slider turtles have this. Oh yeah, and when you feed your turtle, feed him things like shrimp, lettuce, strawberry's, turtle pellets. Most of these things you can find at a local Petsmart, or Petco. Good Luck! :]