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