Calculating cost per square foot

You're given the following tables that have information about a real estate portfolio. The tables provide information on building size and total cost.

Table: building_info

building_id	sqft	num_rooms	num_bathrooms
1	40073	40	10
2	98003	98	25
3	12092	12	3
...	...	...	...

Table: building_cost

building_id	rent	janitorial
1	184314	2654
2	65486	1372
3	52891	2145
...	...	...

Using the tables above, write a SQL query that calculates the average total cost per square foot for each building. In the "building_cost" table you'll have to add both the rent and the janitorial cost in order to calculate total cost.

You can view/query the data in an interactive SQL fiddle here.