An economist estimated the learning curve for the production of Tesla vehicles to be: AC = 433,094*N -0.135 where AC = average production cost and N = cumulative production.

Data used was annual. Calculate the resulting learning rate. From this, we can conclude that

a)AC declines about 9 percent per year due to learning.

b)there are economies of scale in production.

c)there is no learning effect.

d)AC declines about 13.5 percent per year due to learning