A Heat-Conducting Rod, 0 $0.00040 \mathrm {~m} ^ { 2 }$

A heat-conducting rod, 0.90 m long and wrapped in insulation, is made of an aluminum section
that is 0.20 m Iong and a copper section that is 0.70 m long. Both sections have a cross-sectional area of $0.00040 \mathrm {~m} ^ { 2 }$ The aluminum end and the copper end are maintained at temperatures of $30 ^ { \circ } \mathrm { C } \text { and } 230 ^ { \circ } \mathrm { C }$ respectively. The thermal conductivities of aluminum and copper are 205 W/m . K (aluminum) and $385 \mathrm {~W} / \mathrm { m } \cdot \mathrm { K } \text { (copper) . }$ What is the temperature of the aluminum-copper
junction in the rod with steady state heat flow?

A) $80 ^ { \circ } \mathrm { C }$
B) $100 ^ { \circ } \mathrm { C }$
C) $74 ^ { \circ } \mathrm { C }$
D) $86 ^ { \circ } \mathrm { C }$
E) $93 ^ { \circ } \mathrm { C }$