Answer:

length = 75 cm, width = 37.5 cm

Step-by-step explanation:

Assume that her garden is rectangular

perimeter of a rectangle formula: 2 length + 2 width

2 times 75 (length) = 150

2 times 37.5 (width) = 75

to prove that it's twice the width:

150 divided by 75 = 2

150 + 75 = 225(which is the perimeter of Mary's garden)