Here is the original item:
One day in class, Shantrell rested her head against the
wall (A)
and discovered
(B) that she could hear
the classical music that Professor Nguyen played in his office on the other
side. (C)
The music promplty put her to sleep.
You wanted to do this:
One day in class, Shantrell rested her head against the
wall. And discovered that she could hear the
classical music that Professor Nguyen played in his office on the other
side. The music promptly put her to sleep.
A period after wall makes a problem. And discovered that she could hear ... is a lonely verb fragment, which cannot stand alone as a complete sentence.
You might want to review the rules.