You did 150 joules of work lifting a 120-newton backpack.
a. how high did you lift the backpack?
b. how much did the backpack weigh in pounds?

In the given question, we already know
Work done = 150 joules
Force = 120 Newton
Now we know from the study of physics that
Distance (D) = Work done / Force
(a) To find the height upto which the backpack has been lifted,
D = Work done / Force
   = 150 / 120
   = 15 / 12
   = 5 / 4
   = 1.25
So the backpack was lifted to a height of 1.25 metres.
(b) Now we have the find the weight of the backpack in pounds
We know that 1 pound = 4.448 Newton
So if
4.448 Newton = 1 pound
Then
120 Newton = (120 / 4.448) pounds
                   = 26.978 pounds
So the backpack weighed 26.98 pounds.