7. (50) You want to make a solenoid of radius r and length 6 out of a piece of copper wire of resistance R, length L, and diameter D, that you already have, and power it with a battery of voltage V that you also already have. The solenoid must be wrapped N times around a cylinder without overlapping turns. What is B (an equation) inside the solenoid going to be based on V, L, D, N (turns), R, r, E, and any other parameters geometric or otherwise that you need