Answer:
10.8 kilometers
Explanation:
Perimeter of a triangle equation is P (perimeter)= a+b+c
put 32.4 of the left side of the equation as it is the answer for the perimeter and replace and and b with your first 2 side legnths like this
32.4= 10.8+ 10.8+c
Now we must solve for the unknown side legnth c. To do this we must simplify the right side of the equation first by adding 10.8+ 10.8
32.4= 21.6+c
Now we can subtract 21.6 from the left side to solve for c
10.8=c
Therefore the third side is 10.8 kilometers