Answer:
They will be picked up at 2 yards above sea level
Step-by-step explanation:
Let us consider sea level as reference and positions above sea level as positive and below sea level as negative.
With respect to this reference,
the position of top most point is +17 yards
and the position of lower most point is -13 yards
⇒ The position of midpoint is
= +2
∴ <u>They will be picked up at 2 yards above sea level</u>