Can someone explain why this answer is right? Dilpreet drives a distance of 120 miles in 2 hours. She stops for 1 hour to eat lunch and rest. Then she drives another 150 miles in 3 hours. ANSWER: 54 (why is it not 55?)

The table below shows the approximate masses of a dust particle and a grain of pollen. dust particle 0.000000778 g grain of pollen 0.00000000155 g the mass of a dust particle can be estimated and written in the form a × 10^b, where a = 8 and b = the mass of a grain of pollen can be estimated and written in the form a × 10^b, where a = 2 and b = based on the estimates, the mass of a dust particle is approximately blank times larger than the mass of a grain of pollen.