Final answer:
To calculate the demand using the given equation, substitute the price into the equation to find that at a price of 4, the demand is 292 units.
Step-by-step explanation:
To find the demand when the price is 4 using the demand curve equation q = 300 - 2p, simply substitute the price (p) with 4:
q = 300 - 2(4)
q = 300 - 8
q = 292
So, the demand is 292 units when the price is 4.