Hello, Sofia,
I plotted both functions and colored their ranges. The graph won't fit here, however. Try it yourself if you are having a hard time visualizing the lines.
Maximum y occurs at (0,3) for the y=3-7x line at the left of it's range
Maximum y for y = x2 occurs at (-1,1)
Minimum y for y=3-7x occurs at ( 1,-4)
Minimum y for y = x2 occurs at (-1,1)
I'm a little uncertain to the "absolute value," but if it means the absolute value of y, the point (1,-4) becomes the maximum at (1,4)
Bob