Perimeter signifies the distance around the outside of a figure. We are told that the perimeter of this figure is 42.3 m. Add up the lengths of all the sides, including the one marked "x."
7.8 m + x + 11.9 m + 16.3 m = 42.3 m
Combining the terms on the left: 36 + x = 42.3 (meters)
Then x = 42.3 - 36 (meters). So, the exact value of x is x = 6.3 meters