Bonjour Neil,

I am guessing you are referring to the following question: 

Which of the statements is correct:  «Il y a des visiteurs étrangers à l’hôtel», «Il y a des visiteuses étrangères à l’hôtel»  -> both are correct

The adjectives are "étrangers" and "étrangères" -> singular form "étranger" / "étrangère". This is relevant because it shows how French adjectives ending in -er in the masculine form change to -ère in the feminine form as per the lesson content. 

Whilst the noun "un visiteur" (masculine form) becomes "une visiteuse" (feminine form). Other nouns following the same pattern are: un voyageur (= a traveller) - un voltigeur (= an acrobat)- un voleur (= a thief) ...

I hope this is helpful.

Bonne journée !