Answer
The resistance of the battery is $~0.43~\Omega$
Work Step by Step
We can find $R_b$, the resistance of the battery:
$R_b = \frac{V}{I}$
$R_b = \frac{9.0~V}{21~A}$
$R_b = 0.43~\Omega$
The resistance of the battery is $~0.43~\Omega$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.