Correct Answer - 30
Heat current is same `i_(H) = (70 -0)/(R_(1)) = (100 -70)/(R_(2))`
`rArr (R_(2))/(R_(1)) = 3//7 rArr (K_(1))/(K_(2)) = 3//7`
ltbRgt Heat current is same `i_(H) = (T -0)/(R_(2)) = (100 -T)/(R_(1))`
`rArr (100-T)/(T) = (R_(1))/(R_(2)) = (K_(2))/(K_(1)) = 7//3`
`rArr 300 - 3T = 7T rArr T = 30^(@)C`