\frac{N_{t 1}}{N_{1}} = \frac{U_{t 1}^{2} R}{R U_{1}^{2}} \Rightarrow N_{t 1} = \frac{N_{1} U_{t 1}^{2}}{U_{1}^{2}} = 12, 6 W

${\frac{N_{t1}}{N_1} = \frac{U_{t1}^2R}{RU_1^2} \Rightarrow N_{t1} = \frac{N_1U_{t1}^2}{U_1^2} = 12,6\,\mathrm{W}}$