Classify the following descriptions of constraints as bounds, limitations, requirements, proportional relationships, or balance constraints:

a. Each serving of chili should contain a quarter pound of beef.

b. Customer demand for a cereal is not expected to exceed 800 boxes during the next month.

c. The amount of cash available to invest in March is equal to the accounts receivable in February plus investment yields due on February 28.

d. A can of premium nuts should have at least twice as many cashews as peanuts.

e. A warehouse has 3,500 units available to ship to customers.

f. A call center needs at least 15 service representatives on Monday morning.

g. An ice cream manufacturer has 40 dozen fresh eggs at the start of the production shift.