Starducks Coffee is a local establishment in Portland, OR that has developed a reputation for selling a dark vanilla-tinged coffee (Called Its to Quack for! - or ITQF) that people travel from miles around to buy. For the next two week period, they wish to find the least cost way to mix together their 4 main types of coffee (REG, DARK1, DARK2, VAN) to meet anticipated customer demand of 475 lbs. Their optimal mix can exceed 475 lbs if necessary.

The ITQF mix has some requirements. It must consist of at least 20% of the VAN coffee as a foundation of the unique flavor. ITQF must meet or exceed an average robustness target of 5.7 and an average color target of at least 3.75. From years of experience, there are explicit measures of robustness (RB) and color (CR) on a 1-7 scale for each of the four foundational coffees.

REG has a RB rating of 4.7, a CO rating of 3, and a per pound cost of $4.

DARK1 has a RB rating of 6, a CO rating of 5, and a per pound cost of $4.5.

DARK2 has a RB rating of 6.9, a CO rating of 4.6, and a per pound cost of $6.

VAN has a RB rating of 3.2, a CO rating of 2.1, and a per pound cost of $4.85.

Additionally, for the next two weeks, there is an unlimited supply of REG and VAN coffee to use, but only 150 pounds of DARK1 and 200 lbs of DARK2.

Find the optimal way (least cost) of blending together the ITQF coffee for the next two week period.