Struggling to do the second part. Until now, I found -4x-y-3z-6 = 0 but I don't know how to adapt this answer into second part.

Agreeting card company can produce a box of cards for $7.50. if the initial investment by the company was $50,000, how many boxes of cards must be produced before the average cost per box falls to $10.50?

If f(x)=-x^2+6x-1 and g(x)=3x^2-4x-1,find(f+g)(x)

Last one and the bottom answer choice is y=(x-4)^2+1 you guys!