9514 1404 393
Answer:
 -2900 ft
Step-by-step explanation:
We normally measure altitude as a positive number upward from the ground. Then a descent is a negative change in altitude.
To find the total change in altitude, add the changes:
 (-1500) +(-1400) = -(1500 +1400) = -2900
The change in altitude relative to the original altitude was -2900 feet.