What is the slope if its just a straight line going across the graph

There is no slope if the line is straight 

|T-58 | ≤ 15   -15 ≤ T - 58 ≤ 15  +58.     +58     +58    43 ≤  T  ≤  73 Graphing: Draw a solid point on a number line at 43, shade to the right of this point Draw a solid point on a number line at 73, shade to the left of this point The shaded part between the two points represents the temperature the fish can tolerate.