Forraisins葡萄干,thedemand schedule can be represented by the e

Forraisins葡萄干,thedemand schedule can be represented by the equation Qd=1500-300P,where Qd is the quantitydemanded and P is the price.The supply schedule can be represented by theequation Qs=350+700P,whereQs is the quantitysupplied.
其中两条等式表示什么?