Question 117320
FIRST YOU NEED TO FIND THE SLOPE:
SLOPE=(Y2-Y1)/(X2-X1)
SLOPE=(-1-7)/(5+3)
SLOPE=-8/8
SLOPE=-1 
USING THE SLOPE (m) AND A SET OF (X,Y) VALUES IN THE LINE EQUATION Y=mX+b SOLVE FOR (b), THE Y INTERCEPT. 
7=-1*-3+b
7=3+b
b=7-3
b=4
THUS THE EQUATION IS:
Y=-X+4