Suppose a cafe with two espresso machines and one barista is very busy and customers are lined up. The one barista can produce 40 coffee products per hour. The owner hires a second barista and total product increases to 70 units per hour; a third barista is hired and total product increases to 85 units per hour. In terms of labour, this firm is experiencing

a) diminishing marginal returns.

b) increasing marginal returns.

c) constant marginal returns.

d) diminishing total returns.

e) increasing average returns.