We have the next information
2/3 of an hour --- Monday
5/6 of an hour --- Tuesday
3/4 of an hour ----Wednesday
we need to sum each value
as we can see we can't sum the factions above without changing the denominator to a minimum common multiple, in this case, is 12, always we sum fractions we need to have the same denominator
Having all the fractions with the same denominator we can sum them
the time he spent on homework for the week is 9/4 hour or 2 1/4 hours