Question

about 3 cm
shorter than 9 cm
longer than 18 cm
between 9 and 18 cm

Explanation:

Step1: Estimate number of paper - clip lengths

Count that the object is about 3 paper - clip lengths long.

Step2: Calculate length range

Since each paper - clip is about 3 cm long, the length of the object is about $3\times3 = 9$ cm. But visually, it seems a bit shorter than exactly 3 full paper - clip lengths. So it is shorter than 9 cm.

Answer:

Shorter than 9 cm