SOLUTION: the perimeter of a rectangle must not be greater than 30 cm and the length must be 8cm. What is the set of values of the width?

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let the length of the rectangle = l
and the width of the rectangle = w

perimeter <= 30
2*l + 2*w <= 30
(divide both sides by 2)
l + w <= 15
so, if l = 8 then
8 + w <= 15
w <= 15 - 8
w <= 7

so the width must not greater than 7 cm, or it can be said that the width is greater than 0 cm but less or equal with 7 cm (0 < width <= 7cm)