Answer:
price elasticity of demand = % change in quantity / % change in price
-0.75 = % change in quantity / 2%
-1.5 = % change in quantity
lets assume that 1,000 units of X were sold at $40 each, total revenue = $40,000
new total revenue = 985 x $40.80 = $40,188
revenue generated by good X will increase by 0.47%, from $40,000 to $40,188
price elasticity of demand = % change in quantity of Y / % change in price of X
-1.7 = % change quantity of Y / 2%
-3.4% = % change quantity of Y
lets assume that 1,000 units of Y were sold at $90 each, total revenue = $90,000
new total revenue = 966 x $91.80 = $88,678.80
revenue generated by good Y will decrease by -1.47%, from $90,000 to $88,678.80