Formula- Area = L • W
So...
Length = 18 + 3
Width = 18 + 3
Since you’re adding 18 + 3 for Length AND Width, you’re going to get a sum of 21 for each.
Length = 21
Width = 21
Now you’re gonna want to multiply 21 by itself.
21 • 21 = 21 + 420 = ?
Which leaves you with the final sum of...
Area = 441 yds.