Final answer:
The variable e represents the change in elevation, specifically a decrease by 40 units.
Step-by-step explanation:
The equation e + 290 = 250 represents the situation described. To determine what the variable e represents, we need to isolate it on one side of the equation. Subtracting 290 from both sides gives us e = 250 - 290. Simplifying further, e = -40. Therefore, the variable e represents the change in elevation, or in this case, a decrease in elevation by 40 units.