The correct answer is "fifteen designs"
Step-by-step explanation:
In paraphrasing a text, most ideas are expressed using different words and terms from the ones in the original text. However, specific information, such as numerical details or proper names cannot be modified because this would change the original ideas, which is not appropriate. This implies in the text presented, most of the ideas can be modified except by details such as "William Lamb", "18 months" and "fifteen designs". According to this, the correct answer is "fifteen designs".