For this case we have to:
x: Represents the unknown number
y: Represents the exponent of base 10
So, considering a system of equations we have:

From the first equation we have:

Substituting in the second equation:

We choose the positive value:

So, the number is 0.4.
So:

Thus, the exponent is 5.
Answer:
Yara use 0.4 and
Mrs.Kennedy can divide 315 by 10 and then when she gets her answer she can round up to get her answer.
Can you post the question or image
Zero depending on what axis it’s on
I think the answer is C and D..searched it up