The answers are :
y = 3ˣ ⇒ b
y = 3⁻ˣ ⇒ a
y = -3ˣ ⇒ c
For y = 3ˣ, we will get a graph that will increase exponentially in the direction of positive y-axis.
For y = 3⁻ˣ, we will get a graph that will decrease exponentially in the direction of positive x-axis.
For y = -3ˣ, we will get a graph that will decrease exponentially in the direction of negative y-axis.