Answer:
Substitute goods.
Step-by-step explanation:
Last month sales of good Y = 50 units
With higher prices,
This month sales of good Y = 40 units
So, there is a fall in the sales of good Y with higher prices.
At the same time,
Sales of good X increases from 20 units to 40 units, even at the same price level.
Hence,
Good X and Good Y are substitute goods. This is because of the positive cross price elasticity of demand. This means that as the price of good Y increases then as a result the quantity demanded for good X increases. This indicates that there is a positive relationship between the price of good Y and the quantity demanded for good X.