The formula for area of a triangle is 1/2bh. That means that the answer is the base multiplied by the height divided by 2. You can multiply 54 by 2. It gives you 108. If you divide 108 by 12, it gives you 9 (the base). If you plug in all of those numbers, it will give you something like this:
height= 12 area=54 54*2= 108 108/12=9
1/2* 9* 12 = 54
That is extra proof, but the base of the triangle is 9.
