So you have 2 points (0,38,880) and ( 2, 24,319). For linear decay we have a straight line so all you need to do is calculate the slope (24,319 -38,880)/2= -7280.5
Equation the is y = -7280.5x + 38880
For exponential decay need to calculate decay factor
24,319 = 38,880(r^2) r= .7909 so equation is
y= 38,880(.7909)^t
I will leave it to you to graph and analyze the equations