Answer:
$80
Step-by-step explanation:
In this company, every dollar spent in labor has equal marginal product than every dollar spent in capital.
If we spent an additional $20 in labor and the marginal product output is $40, it is a 1:2 relationship (for every dollar spent in labor we get $2 of product output).
If the company spends $40 in capital, if it has the same marginal product output as labor (1:2 relationship), then its marginal product output will be $80.