Answer:
She put 7/24 extra cups of sugar
Explanation:
we know that
To find out how many extra cups did she put in, subtract three and five sixths cups of sugar from three and nine eighths cups of sugar.
so

Convert mixed number to an improper fraction


The LCM between 8 and 6 is 24
substitute the values

therefore
She put 7/24 extra cups of sugar