Question

The grocery store is located at a point on a coordinate plane with the same y coordinate as the bank but with the opposite x coordinate the grocery store and the bank are reflections of each other across which axis

Answer 1

The vertical axis on a graph is the y-axis and the horizontal axis is the x-axis. Keeping this in mind, if they have the same y coordinate that means vertically they are on the same level but their x coordinates are opposite each other, this means 2 things:
1. they are not on the same level horizontally 
2. you have to cross the vertical (y) axis to get from one point to the other.

So to answer your question, These two points are reflected across the y axis.

Hope this helps.