Answer shown and explanation above! Hope this helps!
Answer:
-8
Step-by-step explanation:
(7)*(-8) = -56
(-56) - (-8) = -48
She would have to score atleast a 74 on the test for her average to be 78
Assuming the sheet is a square
see diagram
the length will be 20-2x
the width will be 20-2x
and the height will be x
the volume will be (20-2x)(20-2x)(x)