Given:
Perimeter of the triangle = 99 ft
Length of two sides are 20 ft and 42 ft.
To find:
The length of missing side.
Solution:
Let the missing side be x.
Perimeter of a triangle is the sum of all sides of that triangle.
[tex]x+20+42=99[/tex]
[tex]x+62=99[/tex]
Subtract 62 from both sides.
[tex]x=99-62[/tex]
[tex]x=37[/tex]
Therefore, the missing side of the triangle is 37 ft.