Can someone please explain to me this: Direct Variation and Linear Functions
Best explanaion will get brainliest. I don't really understand this so please explain it well. And Thanks to anyone who can spare some time to help!

What is the equation of the graph that represents f(x)=x^4 stretched vertically by 2 and shifted up 3 spaces

Last year, a state university received 3,560 applications from boys. of those applications, 35 percent were from boys who lived in other states. part a)how many applications did the university receive from boys who lived in other states? part b)applications to the university from boys represented 40percent of all applications. how many applications did the university receive in all? i don't how to do part b so me and plz tell how you got your answer

Jada has a meal in a restaurant she adds up the prices listed on the menu for everything they ordered and gets a subtotal of $42.00. when the check comes, it says they also need to pay $3.99 in sales tax. what percentage of the subtotal is the sales tax