Answer: The expression which represents the condition described is given as 
Step-by-step explanation:
Since we have given that
Amount that Molly owes her brother = $300
Let the number of hours she worked as a checker be x
Cost of per hour = $10
Amount she get after doing work for x hours is given by

Rate of tax are taken out = 80%
So, amount she left with is given by

So, Molly plans to repay her brother half of what she earns is given by

According to question,

So, the expression which represents the condition described is given as

1800:60=30 revolutions per second
30*2π=60π radians per second
Answer:
this answer is 3 for b i got it right