Answer:
27
Step-by-step explanation:
Since the total area is 243, we plug that in to the given equation and get 243=1/2(b)(h).
Then we plug in 18 to the height and get
243=1/2(b)(18)
Then solve for b
243/18=1/2(b)(18)/18
13.5=1/2(b)
13.5/1/2=1/2(b)/1/2
27=b
