Q.The demand function for a good is $Q_d = 200 - 4P$ and the supply function is $Q_s = -40 + 6P$, where $P$ is the price in ₹ and $Q$ is the quantity. Both are linear functions of $P$. Find the equilibrium price and the equilibrium quantity, i.e. the point at which $Q_d = Q_s$.

Market equilibrium is where the two linear functions are equal; set Qd = Qs and solve for P, then substitute back to find Q. …

Setting demand equal to supply.

Equilibrium quantity. Substituting $P=24$ into the demand function:

$Q_d = 200 - 4(24) = 200-96 = 104$ …

Sign errors while moving terms across the equation (e.g. writing 200 − 40 = 6P + 4P instead of 200 + 40 = 6P + 4P). Also, checking the answer using only one of …