#### Answer

perimeter = 18 yards

#### Work Step by Step

RECALL:
(1) The perimeter of a polygon is equal to the sum of the lengths of all its sides.
(2) An equilateral triangle has three side with equal lengths.
This means that the two unknown side lengths of the triangle are both $6$ yards.
Add the lengths of all the sides to find the perimeter:
perimeter = $6+6+6= 18$ yards