Nussult number variation with temperature

Question

The non-dimensional fluid temperature profile near the surface of a convectively cooled flat plte is given by $\frac{T_{w}-T}{T_{w}-T_{\infty }}=a+b\frac{y}{L}+c\left ( \frac{y}{L} \right )^{2}$  ,  where y is measured perpendicular to the plate, L is the length, and a, b and c are arbitrary constants. T_w and $T_{\infty }$ are wall and ambient temperatures, respectively. If the thermal conductivity of the fluid is k and the wall heat flux is q”, the Nuzzelt number $N_{u}=\frac{q}{T_{W}-T_{\infty }}\frac{L}{K}$   is equal to                 

      (a) a                                (b) b                             (c) 2c                              (d) (b+2c)