Correct Answer - C
The given equation can be shown as
Rate of flow of heat will be equal in both the slabs
`therefore (12-x)K_(1)= K_(2) (x-0)`
`12-x = 2x rArr x=4^(@)`C `(therefore K_(1) = (K_(2)/2)`
The temperature difference across slab
`A = (12-x) = (12-4) = 8^(@)`C