Problem with Energy Transfer Rate Conversion

Given the question:

Calculate the energy transfer rate across a 6 in wall of firebrick with a temperature difference across the wall of 50 °C. The thermal conductivity of the firebrick is $0.65 frac{text{Btu}}{text{hr ft }^circtext{F}}$ at the temperature of interest.

The correct answer is 369 W/m²

---

I used the following approach:

$${ x = 6in => 0.5ft }$$
$${ triangle T = 50^oC => 122^oF }$$
$${ k = 0.65Btu/hr-ft-F }$$

$${ frac{Q}{A} = frac {ktriangle T}{x} = 158.6Btu/hr*ft^2 => 500W/m^2 }$$

But I did not calculate the correct answer. Is there a step that I am missing?