Thermodynamics Part 3

As per the given figure, two plates A and B of thermal conductivity K and 2K are joined together to form a compound plate.
The thickness of plates are 4.0‌cm and 2.5‌cm respectively and the area of cross-section is 120cm2 for each plate. The equivalent thermal conductivity of the compound plate is (1+‌

5

α

)K, then the value of α will be______