Calculating elasticity: Draw a set of coordinate axes on a piece of graph paper. Label the horizontal axis from 0 to 50 units and the vertical axis from $0 to $20 per unit. Draw a demand curve that intersects the vertical axis at $10 and the horizontal axis at 40 units. Draw a supply curve that intersects the vertical axis at $4 and has a slope of 1. Make the following calculations for these curves, using the midpoint formula:

1. What is the price elasticity of demand over the price range $5 to $7?
2. What is the price elasticity of demand over the price range $1 to $3?
3. What is the price elasticity of supply over the price range $10 to $15?
4. What is the price elasticity of supply over the price range $15 to $17?

These are the answers:

1. 1.5
2. 0.25
3. 1.47
4. 1.33

I don't understand how to solve these problems. Could you please help me with the answer and explain me why and how to calculate it.

Thank you