#### Answer

195 dollars

#### Work Step by Step

We first must find the values of $H$ for both the wall and the roof. Doing this, we obtain:
$H_{roof} = \frac{1}{12.65} (1506)(50) = 5953 \ Btu/h$
$H_{wall} = \frac{1}{31.65} (\frac{36\times28}{cos30^{\circ}})(50) = 1839 \ Btu/h$
Adding these, we get $7792 \ Btu/h$, which is the same as 56.1 gallons per year. Since each gallon costs 3.48 dollars, we find that it will cost $\fbox{195}$ dollars.