In the spring, a 17-rung ladder is placed against Santa Claus's house.
The rungs are spaced 15 cm apart.
During winter, snow falls at a rate of 30 cm per hour.
Question:
After 3.5 hours of snowfall, how many rungs remain uncovered by the snow?

Answer:
10 rungs
3.5 hours = 7 half-hours
So, 7 rungs in 3.5 hours.
17 - 7 = 10 rungs