Answer:
$200
Explanation:
This is a perimeter problem. In order to calculate how much trim you need, you need to know the distance all the way around the room, so add up all four sides.
P = 13 + 12 + 13 + 12
P = 50
You will need 50 feet of trim to go all the way around the room (I guess for real life, there's at least one door, but that extra could be the "in-case-of-a-bad-cut" extra!) We'll keep it simple here though.
If you need 50 feet of trim and it costs $4.00 per foot, then multiply.
Cost = 50 * 4
Cost = 200
The trim will cost $200.00. (not including tax or if it is only sold in 12 ft lengths or any other complicating issues)