Answer
$a.\quad x=4$
$ b.\quad x \geq 4$
Work Step by Step
$a.$
Graph $y=-2x+3$ (red on the image)
and $y=3x-7$ (blue).
The solution (if it exists) is the x-coordinate of the intersection.
Solution: $x=4$
$b.$
Using the graphs of part (a), we see that
the red graph is below or intersecting the blue graph when $ x \geq 4$