Answer:
We need first to calculate how much the quantity demanded changed
The quantity of fish demanded with a revenue of $1,500 at $5 per fish is equal to:
$1,500/$5 = 300
For a revenue of $1,800 at $9 per fish:
$1,800/$9 = 200
Now we can calculate the price elasticy of demand. Remember the formula
PED = ΔQuantity /ΔPrice
ΔQuantity = Q2 - Q1 / Q1
Where Q1 is the old quantity demanded and Q2 is the new quantity demanded
ΔQuantity = 200 - 300/300
= -0.33
ΔPrice = P2 - P1/P1
Where P1 is the old price and P2 is the new price
ΔPrice = 9 - 5/5 = 0.8
Now we can finally calculate the price elasticity of demand
PED = -0.33/0.8
= -0,4125