use the midpoint formula. It's x1 + x2 / 2, y1+y2/2. When you solve you get (0, 1/2) is the midpoint. Hope this helps
Answer: 
Step-by-step explanation:

if it matters then simply further...
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Answer:
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Step-by-step explanation:
The point slope form of a line is written as y - y1 = m(x -x1)
Where m is the slope and x1 and y1 are the points on the line.
You are told the slope is 3 and the point is (2,-1/2)
x1 is 2 and y1 is -1/2
Replace those in the equation to get:
y- (-1/2) = 3(x-2)
Simplify to get the final answer:
y + 1/2 = 3(x-2)