If n>0 and 9xsquared + kx + 36= (3x + n)squared, for all x, what is k-n?

another question i needed to check is this one:

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A family of five adults and two children are trying to cross a river. They have a lifeboat which can ONLY carry one of the following:

A) One Child

B) Two Children

C) One Adult

The boat may not carry two adults or a child and a adult

How many one-way trips for the entire family to cross the river.

How many one-way trips are required for a family of 1000 adults and two children

someone plz answer im a newbie so someone help me plz