Two groups of hikers start at the same time and hike at the same average speed. marks group hikes for 2.5 hours. sally’s group hikes for 4.7 hours and covers another 7.7 miles. write and solve an equation to find how fast the hikers are going

You know that in physics, the average speed is the ratio of distance covered at a certain period of time.

Speed = Distance/Time

If the problem indicated that the two groups have equal average speeds,
Speed of Mark's Group = Speed of Sally's Group

Now, the problem also indicates that the time is equal. That means the time it took for Sally's group to cover the additional 7.7 miles is,
t = 4.7 - 2.5 = 2.2 hours.

Then, that means the speed is,
Speed = 7.7miles/2.2hours = 3.5miles/hour