Aman can clear his driveway using a snowblower in 45 minutes. it takes his son 2 hours to clear the driveway using a shovel. about how long would it take them to clear the driveway if they worked together?

Father's rate: 1/45 (driveways/minute)
Son's rate: 1/120 (driveways/minute: 2 hours equals 120 minutes)
combined rate: 1/45 + 1/120 = 11/360 (driveways/minute)

time at combined rate: 1/(11/360) = 
360/11 minutes =
32.73 minutes, which is about 33 minutes

If i think this is what your asking, he should look at the grams or pounds/ounces and compare the to their cost then max can identify which one is proportional and which is not ( i think xd)