1.
[tex]Dane:\\R = 6 \ \Omega\\I = 3 \ A\\Szukane:\\U = ?[/tex]
[tex]Z \ prawa \ Ohma\\\\R = \frac{U}{I} \ \ \rightarrow \ \ U = R\cdot I\\\\U = 6\Omega\cdot3 \ A = 6\frac{V}{A}\cdot3 \ A\\\\\boxed{U = 18 \ V}[/tex]
2.
[tex]Dane:\\I = 3 \ A\\U = 25 \ 000 \ mV = 25 \ V\\Szukane:\\R = ?[/tex]
[tex]R = \frac{U}{I}\\\\R = \frac{25 \ V}{3 \ A} = 8,(3) \ \Omega\\\\\boxed{R \approx8,3 \ \Omega}[/tex]