So,
Let s represent the time Mo-Qui spent studying Spanish and h represent the time Mo-Qui spent studying History.
s = h + 30
s > 2 hrs. 15 mins. (he isn't done yet)
Substitute
2 hrs. 15 mins. = h + 30 mins.
Subtract 30 mins. from both sides
1 hr. 45 mins. = h
However, s > 2 hrs. 15 mins., so h must be more than 1 hr. and 45 mins.
h > 1 hr. 45 mins.
Is this what you were looking for?