Answer:
36 kg/h
Step-by-step explanation:
We start calculating the total amount of square feet of the lawn with the rectangle area equation:
Area(rectangle)= long x wide = 20 ft x 16 ft = 320

Now, for every one of those 320
1250 new snowflakes accumulates each minute, this means that means that in one minute we get:
# Snowflakes (min) =

In a minute we have 400,000 snowflakes, then we need to multiply that by the number of minutes in an hour (60 min in an hour):
# Snowflakes (hour) =

If each snowflake has a mass of 1.50 mg (the average), then:

In each kilogram there are 1000000 mg so making this transformation:
36,000,000mg to kg ⇒
