"Also, how do you make a 5% solution out of the 28% solution?"
If you divide 5% into 28% you get 5.6
So a 28% solution is 5.6 times stronger than a 5% solution.
So you should be able to take a certain amount of Miracle-Mineral-Supplement and multiply that volume of liquid by 5.6
For example you could take the whole 5.5 ounce bottle of Miracle-Mineral-Supplement and pour it into a measuring container. If you multiply 5.5 ounces by 5.6 you would get 30.8 ounces.
Do you honestly want to carry around a gigantic 30.8 ounce bottle instead of learning how to mix the 28% solution in a convenient little 5.5 ounce bottle?