英语数学题我晕For problems 1and 2 ,the supply and demand equations

英语数学题我晕
For problems 1and 2 ,the supply and demand equations are given as follows :
S=2/3P-100 D=-4/3P+500 ,where P is the price
The equilibrium price is
A 200 B.300 C.600 D.900
2. The number of items that wil be demanded at the equilibrium price is
A.500 B.300 C.200 D.100




正确：B D

主要不懂 ,where P is the price
求讲解 求详解 求算法 求 equilibrium price 平衡价格?的意思