They will be there for 40 minutes because 25+15 is 40
1. Each term in this polynomial has a common factor of
:

2. Not sure what the "vertical method" is, but I would guess it refers to some way of visualizing the distributive property.



3. You can use the same approach as in (2), or recall that
:


4. Recall that a difference of squares can be factored as
. So


Try this solution:
1. according to the condition

2. for more details see the attached graph.
Answer: [0;+oo)