Watch the following video for a tutorial.
On your smartphone, download the free Adobe Scan Digital app from the App Store.
In the app, select document and hover over your page.
You should see blue dots at the four corners of the page.
Click "Continue".
Click "Save as PDF".
It is now saved to your camera roll in your phone.
Open the assignment asking for a scan or photo in Google Classroom.
You can do this directly from your phone if you download the Google Classroom app from the App Store.
Select "Add Attachment" and select your scanned photo.
If you are using your computer to submit the assignment, you'll need to send the picture from your phone to your computer (via email, google drive, etc.).
Don't forget to click submit!