The following are 24 thumbnail sketches I created for the project.

Thumbnail Set 1

Thumbnail Set 2

Thumbnail Set 3
Next, I developed thumbnails 8, 24, and 24 in Adobe Illustrator.

Final Design 1

Final Design 2

Final Design 3
After that, I found a picture of a blank T-shirt at Pexels.com and created T-shirt mockups for each design. T-shirt mockup photo by Mr. Mockup: https://www.pexels.com/photo/a-blank-white-shirt-12025472/

Final T-Shirt Mockup 1

Final T-Shirt Mockup 2

Final T-Shirt Mockup 3