Answer: 2
See the diagram below.
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Step-by-step explanation:
Pick two points on this diagonal line. I'll go for (0,-3) and (1,-1)
Apply the slope formula to those coordinates.

A slope of 2, aka 2/1, means "move up 2, then right 1".
This "up 2, right 1" motion allows us to move from (0,-3) to (1,-1) as shown in the diagram below.