Answer:
[tex]-12x^2[/tex]
Step-by-step explanation:
Think of the box method as completing a chart or a multiplication table.
We can see that box B is in the second column of the first row. The second column is labeled by -4x. The first row is labeled by 3x. So, in order to fill out box B, you have to multiply -4x and 3x together.
To do so, multiply the terms' coefficients (the numbers in front of the variable). -4 times 3 makes -12. Then, multiply the variables - just keep the variable and add their exponents. x and x both have exponents of one, which makes [tex]x^1^+^1[/tex], resulting in [tex]x^2[/tex]. Put them together and the answer would be [tex]-12x^2[/tex].
