
Let
, so that differentiating both sides wrt
gives

If
and
, the above reduces to

This is the slope of the tangent line, which has equation

Answer:
140 minutes
Step-by-step explanation:
After 28 mins you've gone 4 miles, assuming this rate is constant and you dont slow down or speed up, in order to get to 20 miles you will have run 5x as much (20/4 = 5), thus 5x the amount of time (28x5).
20/4 = 5
5x28 = 140
219 divided by 8=27.35
27x8=216
219-216=3
Matthew can make 27 packages.
3 pens will be left over.
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