If I understand correctly you want to convert each of these to fractions? I like to do this by using a base of 100 and then reducing
Multiply 2.88 by 100 by moving the decimal place over and you get 288
so 2.88 = 288/100
then you can reduce this by dividing top and bottom by 4 to get 72/25
you can do the same thing with 15.88 Multiply by 100 to get 1588
15.88 = 1588/100 = 397/25