9514 1404 393
Answer:
a = 9 meters
Explanation:
The perimeter is the sum of the side lengths:
28 m = a + 2m + a + 8m
18 m = 2a . . . . . . . . . . . . . . . . subtract 10m, collect terms
9 m = a . . . . . . . . . . . . . . . divide by 2
The value of a is 9 meters.