In the following question, the sentence given with blank to be filled in with an appropriate word. Select the correct alternative out of the four and indicate it by selecting the appropriate option.
7 workers work in a printing press. Each gets paid Rs 450 per day. The 8th worker demands Rs 500 per day. If this worker is hired then all other workers must be paid Rs 500. The marginal resource (labour) cost of the 8th worker is _______.