Which adjective would u describe two studious girls a)estudioso b)estudiosos c)estudiosa d)estudiosas

Which of these expressions is the most casual way to greet a friend

Okay so i'm taking an online spanish course (penn foster), and in the study guide, you have to create a bunch of sentences with words you've learned so far. translating, reading, and those kinds of things are fairly easy, but when it comes to making my own sentences, my brain just kinda waltz's away. anyone got any tips?

Sandra is cooking her famous brownies for her class for her recipe she needs 5/7 of a cup of sugar and 1/8 as much salt as sugar how much salt does she need for recipes