A marking on the bottom of a tape recorder specifies that it should be connected to a 6 V and draw 300 mA. 1.

A marking on the bottom of a tape recorder specifies that it should be connected to a 6 V and draw 300 mA.
1. What is the net resistance of the wire?
2. If the voltage drops to 5 V how would the current change?

1. 300 mA.= 0.3 A
R = E/ I = 6 / 0.3 = 20 Ω

2. Resistance remains the same as 20 Ω

I = E/R = 5 / 20 = 0.25 A

Change in current 0.3-0.25 = 0.05 A = 50 mA.
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net resistance of the wire ? You mean including the tape recorder, or just the wire ?
If it's just the wire, you don't have enough information.

If the tape recorder is a linear resistance (unlikely) you could use Ohm's Law

Electronic circuits usually have transistors and diodes inside; these have a forward bias voltage of about 0.6V. So if you connect less than 0.6V, no current flows, and above 0.6V, current starts to flow. That makes the thing non-linear, you won't get exactly 5/6 the current if you supply 5/6 of the voltage.