Box of markers = $ B
Shoulder bag = Twice as much as the box of markers = $ 2B
Pen = Six less than the shoulder bag = $ (2B - 6)
Hence, the cost of pen is $ (2B - 6).
Given function:

The minimum value of the function can be found by setting the first derivative of the function to zero.


Solving for x:


Substituting the value of x into the original function:

Hence, the minimum value in the given range is (-1, -0.368)
When you make the product of a binomial of the kind x + a times other binomial that is of the kind x - a, you obtain another binomial (not a trinomial), so any example with that form will be a counterexample that disproves the conjecture:
(x + a) * (x - a) = x^2 - a^2
For example, (x +3) * (x - 3) = x^2 - 9. So, not always the product of two binomials is a trinomial.
12y+3x-24 you times everything in the bracket by 3