Enclosing the garden means you need to find the perimeter of the garden.
To find the perimeter, you will need to add up all the side lengths.
Rectangles have equal opposite sides.
Add 35 m + 21 m + 35 m + 21 m.
35 + 21 + 35 + 21 = 112
It will take 112 meters of fencing material to enclose the garden.