The cost depend on the number pencils, so the cost is the y and # of pencils is the x
Same as for question 7
To graph, the length depend on the time, so length is y, time is x
6. Linear
7. Not
Idek lol but yeah have a good day

The surface element is

and the integral is


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To compute the last integral, you can integrate by parts:



For this integral, consider a substitution of




and the result above follows.