9.5 Exercise 10

Three 70-kg deer are standing on a flat 200-kg rock that is on an ice-covered pond. A gunshot goes off and the deer scatter, with deer A running at $\left(15 \text{m}/\text{s}\right) \hat{i} + \left(5.0 \text{m}/\text{s}\right) \hat{j}$, deer B running at $\left(−12 \text{m}/\text{s}\right) \hat{i} + \left(8.0 \text{m}/\text{s}\right) \hat{j}$, and deer C running at $\left(1.2 \text{m}/\text{s}\right) \hat{i} - \left(18.0 \text{m}/\text{s}\right) \hat{j}$. What is the velocity of the rock on which they were standing?