Yes, this is very easy thanks to Sketchup’s “inference engine” which is a mechanism to auto-lock the cursor to points of interest in the model. Examples include the endpoints and mid-points of edges and the centers of circles and arcs.
I suggest that the first step is to make a component with the geometry (edges and faces) of one rack. The geometry within a component does not “stick” or merge with geometry from other parts of the model. To create a component of a rack, triple-click on any edge or face of a rack (such as the right-most block in your image, which looks to be slightly isolated from the rest of the model). Then choose Make Component… on either the Edit menu or the right-click context menu (when pointing to the selected geometry). Give the component any name you want such as Rack, and click Create. (You can change the name or description etc. later.)
Then delete the geometry of the other three racks (triple-click on any part of it and press Delete). That stuff will be replaced with copies of the rack component you just created.
To make rack copies and accurately align them next to each other, select the rack component with a single click. The result should be that a blue bounding box is drawn around the rack. Activate the Move tool (e.g., press M).
- Hover the mouse near the upper-right-front corner of the rack component. There should be a purple dot overlaying the corner, which is the inference engine showing that it is targeting that interesting point in the model. If you leave the cursor hovering there for a second, a tool-tip will appear saying “Endpoint in ‘component name’”.
- Click and release. This begins the move operation. If you move the mouse around, the rack should follow the cursor.
- You don’t actually want to move that rack, so press Alt or Option. This tells the Move tool that you want to make a copy of the selected component and move that new copy.
- Move the cursor along the top-front edge of the first (original) rack. The copy being placed should follow the cursor. Move the cursor to the upper-left-front corner of the original rack. A purple dot should appear with the tool-tip (after a second) saying “Endpoint in ‘component name’”.
- Click and release. A second copy of the rack should appear in the model, located exactly “shoulder-to-shoulder” with the first rack.
- If you want to place more racks that have the exact same spacing as the second rack you just created, type “x2” or “x5” or etc. This will cause the Move tool (which must still be active, but idle) to create a total of 2 or 5 or however many new racks (in addition to the first original rack).