Some words in Spanish are just like that. To determine whether it is feminine or masculine, we depend on the definite articles to help us out. Unfortunately, that is not provided in this case. So you really just have to use your best judgement and use the process of elimination to determine your final answer.
If you have any more questions, let me know!
Hope this helped !! :)
Many rules and many exceptions. https://www.spanishdict.com/guide/masculine-and-feminine-nouns
I do not hear the "l" in facil when she says it. When the man says it, I can hear it!
..because facil is already an adjective. "De + adjective" would be like saying "of + adjective" in English, which is grammatically incorrect. Your suggestion would translate to "a class of easy" (if that makes sense). Adjectives directly connect with a noun without a preposition like de, like un sombrero amarillo (not un sombrero de amarillo).
"An" comes before words that begin with a vowel. (except Y) You don't say A avocado A egg A important meeting A oval A underpass A yellow crayon... I guess Y is the exception, but listen to how bad the others sound. "An" should be used before a, e, i, o, u
"Un" vs "una" in Spanish has nothing to do with "a" vs "an" in English at all.
For "un" vs "una", either means "a"/"an" in English, but "un" is for masculine nouns (un momento, un hombre, un niño) while "una" is for the feminine (una clase, una mujer, una niña).
For "a" vs "an", either means "un"/"una" in Spanish but "a" is used for words starting with a consonant sound (a book (b-), a universe (y-), a human (y-)), while "an" is used if it starts with a vowel sound (an eraser (e-), an organ (o-), a honest person (o-)).