Answer:
50 feet
Step-by-step explanation:
Perimeter is the sum of all of the lengths of the sides.
A triangle has three sides, and three lengths are given, therefore all the sides are given.
The sum of the sides is 20 + 20 + 10 = 50
So the Perimeter is 50 feet
Let x = width of border
Area is given to be 7 square feet or 49.
49 = (2x + 2)(2x + 4)
Solve for x.
Option A and Option F
The expressions that represent the perimeter of rectangle are 4s + 1 and 
<em><u>Solution:</u></em>
From figure,
Length = s
Width = 
<em><u>The perimeter of rectangle is given as:</u></em>
perimeter = 2(length + width)
Substituting the values we get,

Thus option F is correct
On further simplification,

Thus Option A is correct