Market for Productive Resources; Earnings, Productivity, and the Job Market

Part 1 
What is the link between marginal revenue product and wages?
Due to there being discrepancies between the productivity and resource offerings (i.e., education, skills, experience) in labor markets, is it justified for one employee with a higher marginal revenue product to earn a higher wage than an employee with a lower marginal revenue product?
Does this notion of marginal revenue product and wages conflict with minimum wage laws?

Part 2
Marginal revenue product is defined as the change in total revenue that results from the employment of an additional unit of a resource. A producer wishes to determine how the addition of pounds of plastic will affect its MRP and profits. See the table attached, and answer each of the questions.

a. The marginal product of the 3rd pound of plastic is ________.
b. The marginal revenue product of the 3rd pound of plastic is ______.
c. The price of plastic is $135 per pound. To maximize profit, the producer should produce
__________________.
d. The price of plastic is $135 per pound. To maximize profit, the producer should buy and use:
________________.