Given : Each Dentalia shell is about 1.5 inches long
⇒ Length of Necklace made with 24 Dentalia shells is (1.5 × 24) = 36 inches
⇒ Length of Necklace made with 18 Dentalia shells is (1.5 × 18) = 27 inches
We can notice that 24 Dentalia shells Necklace is Longer than 18 Dentalia shells Necklace
The Difference of Length of 24 Dentalia shells Necklace and 18 Dentalia shells Necklace gives how much longer the 24 Dentalia shells Necklace is than 18 Dentalia shells Necklace.
⇒ Difference = 36 - 27 = 9 inches
⇒ 24 Dentalia shells Necklace is 9 inches longer than 18 Dentalia shells Necklace