When considering shrinkage or swelling (whether by heat or other agent eg moisture uptake)

First divide into object and surroundings.

Then decide if only the object changes or are the surroundings also affected.

Then consider is the expansion free or constrained in any way.

Then find the longest dimension in the object (this may not be in a straight line)

Finally you can apply the linear expansion coefficient, which you may need to do in mutually perpendicular directions.

Can you now at least make a start on this question?