Respuesta :

the answer is C, i’m a math teacher

Answer:

The correct Answer is 9 my good sir ( or ma'am )

Step-by-step explanation:

Simple, just flip the equation around and change the multiplication sign to a division sign.

So basically with all planks filled in its 9 times 3.5 which is equal to 31.5

Brianliest? :/

Hope I helped