Question 252388
you have too many questions lumped together.
I'll answer one of them
(2x+3)(x+k)=2x^2+13x+15
k=?
let's multiply out the two factors using foil
2x^2 so far so good
now inner and outer
2xk+3x
last 
3k
my first guess is that k=5
since 3*5=15 and we have 3k as the final term
subtract3xfrom 13x we get 10 x
so 2xk is 10x
so k is indeed 5