How to solve unknown using calculus?

Question

Can someone please explain to me how to do question 5? Thanks!

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Answer 1 · 2017-09-25T15:48:18

Please see below.

The function #f(x) = x^3-9x^2+15x#

Has a local maximum of #7# at #x=1# and a local minimum of #-25# at #x=5#.

The graph is:

graph{x^3-9x^2+15x [-18.43, 32.9, -12.87, 12.8]}

In order to eliminate two of the zeros, we can either translate up by more that #25#, so use #w > 25#

or we can translate down by more than #7#, using #x < -7#