I have three questions plz medals!!

5) The ordered pairs (1, 3) (2, 9) (3, 27) and (4, 81) represent a function. Write an equation that represents this function.

6) The ordered pairs (1, 1) (2, 16) (3, 81) and (4, 256) represent a function. Write an equation that represents this function.

7) You want to buy your friends some $25 i-tunes gift cards. You have a $10 off coupon for the total purchase. Write a function to represent the cost of the gifts. What would be the cost of 8 gift cards?

Question

I have three questions plz medals!! 

5)	The ordered pairs (1, 3) (2, 9) (3, 27) and (4, 81) represent a function. Write an equation that represents this function.

6)	The ordered pairs (1, 1) (2, 16) (3, 81) and (4, 256) represent a function. Write an equation that represents this function.

7)	You want to buy your friends some $25 i-tunes gift cards. You have a $10 off coupon for the total purchase. Write a function to represent the cost of the gifts. What would be the cost of 8 gift cards?