The perimeter of a rectangle is given by
p = 2(length + width)
You want to find the width when
p > 84 cm and length = 16 cm.
Substituting for p and for length,
2(16 cm + width) > 84 cm (the result of substituting the given information)
16 cm + width > 42 cm (divide both sides by 2)
width > 26 cm (subtract 16 cm from both sides)
Rectangle widths greater than 26 cm will make the perimeter greater than 84 cm for the given length.
p = 2(length + width)
You want to find the width when
p > 84 cm and length = 16 cm.
Substituting for p and for length,
2(16 cm + width) > 84 cm (the result of substituting the given information)
16 cm + width > 42 cm (divide both sides by 2)
width > 26 cm (subtract 16 cm from both sides)
Rectangle widths greater than 26 cm will make the perimeter greater than 84 cm for the given length.