Question

Number 6-9 I don't know it

Answer 1

This is not 4 different problems.
It's the same problem 4 times.

The Rule:  To find the unit rate, divide the price by the quantity.
                 Just like you wrote in pencil next to  #6  and  #8 .
_________________________________

#6).  Look at The Rule up above.

       Unit price for Brand A:    $4.80 /  32 oz  =  15¢ per oz.
       Unit price for Brand B:    $5.76 /  48 oz  =  12¢ per oz.
       Unit price for Brand C:  $17.92 / 128 oz  =  14¢ per oz.

#7). 
IF the price is the ONLY thing that's different about them, then Brand-B 
is the best choice, because it's the lowest price per ounce.

BUT ... there may be other things to compare:
Do they all get your dishes equally clean ?
Do they all rinse off equally easily ?
Do they all smell the same ?
Do any of them attract bugs when they stand around ?
Do any of them spoil when they stand around open ?

You may want to consider other things besides the price
when you're deciding which detergent to buy.

#8).  Look at The Rule up above again.

       Unit rate for Regular size = $3.36 / 16 oz  =  21¢ per oz.
       Unit rate for Family size  =  $7.60 / 40 oz  =  19¢ per oz.

#9).
Again ... IF the cost is the ONLY thing to think about, then the Family size
is the better buy, because it costs 2¢ less for every ounce. 
But there may be other things to consider.  Does the peanut butter from
both sizes taste the same ?  Does one taste better ?  Is the Family size
so big that it might be hard to handle, and you may drop it by accident ?