I would approach the problem like this:
1 oz bottle.............................30cm^3
33 oz bottle.............................xcm^3
in a 33 oz bottle will be x=33*30=990cm^3
density=mm/v
13.6g/cm^3= m/ 990cm^3
m= 13.6 * 990=13464 g
or 13.464 kg in a 33 oz bottle
In order to write 25 letters in 4 days you would need to write 6.25 a day
