I’m not sure about the estimates but the overall answers should be correct
See attachment although I gather this is not your question. I did the graph(s) for the function,
M(x, y) = ((x1 + x2)/2, (y1 + y2)/2) = ((-2 + 4)/2, (5 - 9)/2) = (2/2, -4/2) = (1, -2)
What is the question that you are asking? Do you need to write an equation?