In which sentence is the number written correctly?
a. the water temperature at the beach is sixty-eight degrees.
b. my uncle will turn thirty one on tuesday.
c. we donated twenty six bags of clothes to a charity.

A: The water temperature at the beach is sixty-eight degrees.

There are two general rule:

   - since you are consistent in spelling the numbers out, you must put a hyphenate on the numbers

   - typically if you have a number greater than ten you put it in number form (ie 13) instead of word form. It just depends of your preference as a writer or what the teacher wants.

Hopefully this helped and good luck.

“way of writing” should be replaced with “writing style"

“idea” should be replaced with “purpose.”

maybe   “people from a long time ago” should be replaced with “elizabethans.”