Right answer is (b) 2

The best I can explain: Let Tx be temperature gradient developed at the surface. If the heat transfer coefficient at the surface of a wall is is 9\(\frac{W}{m^2K}\) then the heat interaction at the surface of the wall is evaluated by equating the conduction heat transfer to the convection heat transfer, i.e.,

45Tx = 9(35-45)

Tx = \(\frac{9}{-45}\) (35-45)

=\(\frac{1}{-5}\) (-10)

=2.