R 150 A R3 R R A Wheatstone Bridge is used to determine the value of an unknown resistance R4 as shown in the diagram. The value of R2 is fixed at 22 2. The resistors shown as R1 and R3 are two parts of a uniform resistance wire. The bridge is balanced (i.e. no current flows through the voltmeter, V) when the length of wire corresponding to resistance R is 40 cm and the length of wire corresponding to resistance R3 is 60 cm. Calculate the value of the unknown resistance R4 to the appropriate number of significant figures. R4= x .