There is a segment AZ , with two points at A and middle
Objective is to find point Z
first find slope m of the segment. AM
m = Y/X where Y = y - y'. And X = x - x'
m = (8-9)/(0-(-4))= -1/4
Now find equation of line MZ
y = -(1/4)x + b
replace M(-4,9) to find b. b = 9+(1/4)•(-4)= 9-1= 8
then equation MZ is
y= (-1/4)x + 8
AZ = AM + MZ
then finally
from 0 to -4 there are -4 , so go now another -4 , result -8
so x= -8
from y= 8 to 9 there is 1 , so go another 1 up, result is 10
so y= 10
then finally point Z is ( -8,10)