There are 30 + 15 + 40 = 85 minutes accounted for. She spent 2 * 60 = 120 minutes. She spent 120 - 85 = 35 minutes cleaning her room.
This justifies what answer for what question? Q & A:
Miriam spent 30 minutes doing laundry, 15 minutes cleaning the bathroom, a certain amount of time cleaning her room, and 40 minutes doing homework. If she spent a total of two hours on these tasks, how long, in minutes, did she spend cleaning her room?
35