Which relation is also a function?

What’s the range cuz i can’t find it?

In september, louise planted a tree. every month, the tree louise planted grew 2 inches. what would the constant of proportionality of the line be?

The value, v, of kalani’s stock investments over a time period, x, can be determined using the equation v=750(0.80)^-x. what is the rate of increase or decrease associated with this account? 20% decrease 20% increase 25% decrease 25% increase