constraints

B Chemicals refines crude oil into petrol. The refining process uses two types of crude oil – heavy and light. A mixture of these oils is blended into either Super or Regular petrol.
In the refining process one gallon (g) of Super is made from 0.7g of heavy crude and 0.5g of light crude. One gallon of Regular is made from 0.5g of heavy crude and 0.7g of light crude oil. (There is a refining loss of 0.2g in each case.)

At present, 5,000g of heavy crude and 6,000g of light crude oil are available for refining each day. Market conditions suggest that at least two?thirds of the petrol refined should be Super. The company makes contribution of $0.25 per gallon of Super and $0.10 per gallon of Regular.

Required:
(a) State the objective function and three constraints, one for heavy crude, one for
light crude and one for market conditions.

can you explain what will be the MARKET constraint?