Answer:
-15 would be the answer because if it's below sea level it would have a negative sign in front of 15
Step-by-step explanation:
1.
18 units
10 units right and 8 units up.
2.
7 units
3 units right and 4 units down.
3.
8 units
1 units right and 7 units down
4.
8 units
5 units and 3 units down