Hi Sara,
If the shirt was discounted from $24 to $8 then it was discounted by $16.
The figure what percent the discount was, create a fraction of the discount divided by the original price...
16/24 which reduces to 2/3 by dividing top and bottom by 8.
Now divide 2 by 3 to get a decimal--> 0.666666666666666666666666...
Now move the decimal 2 places to the right to change to a percent . . . . 66.7% discount
The new selling price is $8 according to the question.
Dan