Need Help ASAP! Which relation is a function?

A25-inch wide drum is used in a marching band. what area does the top of the drum cover? round to the nearest hundredth. (use 3.14 for pi.)

The difference of two numbers is 40. find the numbers if 0.3 parts of one number is equal to 37.5% of the other one.

Point r divides in the ratio 1 : 5. if the coordinates of e and f are (4, 8) and (11, 4), respectively, what are the coordinates of r to two decimal places?