Answer:
The simplest form of the given expression is 15b.
Step-by-step explanation:
The given expression is
[tex]6b+9b[/tex]
Which represents the total pieces of product in the boxes [tex]b[/tex].
This expression has two like terms, because both of them have the same variable, and that variable has the same exponent, so they are like terms by definition.
To solve like terms, we just need to sum their coefficients and maintain the variable:
[tex](6+9)b\\15b[/tex]
Therefore, the simplest form of the given expression is 15b.
