When you see "of", think multiplication...
7/8 * 18 = 7/4 * 9 = 63/4 = 15 3/4 = 15.75
7/18
how many eighths are in tree and seven eighths
7/8 of 21 is 18 3/8
seven eighths
seven-eighths
Seven eighths divided by 28.35 = 0.03086419753
Equivalent decimal for seven eighths is 0.875.
It is 49/64.
Neither of your options are correct, it should be seven eights (not eighths) are fifty four.
The answer is seven eighths
31
31 of them.