To find the resistance R2, we can use Ohm's Law, which states that the voltage (U) across a component is equal to the current (I) through that component multiplied by the resistance (R) of the component.

First, we need to calculate the total resistance in the circuit:
Rtotal = R1 + R2 + R3 + R4 + R5 + R6 + r0
Rtotal = 40 + R2 + 25 + 45 + 60 + 60 + 1
Rtotal = 231 + R2

Now, we can use Ohm's Law to find the voltage U across the resistor R2:
U = I Rtotal
U = 6 (231 + R2)
U = 1386 + 6R2

Since the total voltage E in the circuit is given as 156 Volts, we can set U equal to E:
1386 + 6R2 = 156
6R2 = 156 - 1386
6R2 = -1230
R2 = -1230 / 6
R2 = -205 Ohms

However, resistance values cannot be negative, so there might be a mistake in the calculations. Please double-check the values provided and the calculations.