Lin Co$.$ is buying machinery it expects will increase average annual operating income by $$40,000.$ The initial increase in the required investment is $$60,000,$ and the average increase in required investment is $$30,000.$ To compute the accrual accounting rate of return, what amount should be used as the numerator in the ratio?

$$30,000$

$$20,000$

$$60,000$

$$40,000$