R_{234} = R_2 + R_3 + R_4 = 75 + 300 + 300 = 675 \text{ Ом}
R_{56} = R_5 + R_6 = 31 + \text{неизвестно} \text{ Ом}
R_{total} = R_1 + \frac{R_{234} \cdot R_{56}}{R_{234} + R_{56}} = 1000 + \frac{675 \cdot 31}{675 + 31} \approx 1000 + 29.8 \approx 1029.8 \text{ Ом}