Creating a supply / demand graph with two horizontal supply curves

I am trying to make a supply / demand graph in excel which features one demand curve and two horizontal supply curves (i.e., perfectly competitive market, curves before and after removal of a subsidy). In this graph, quantity would be the X-axis and price would be the Y-axis.

I am familiar with how to make a supply / demand graph *if the supply curve is not horizontal*, but the horizontal nature is leaving confused.

The graph would roughly look like the attached image - any help would be really appreciated, thank you!

Hand-drawn Image.jpg