Question 77479
THE SLOPE IS (Y2-Y1/(X2-X1) THUS WE HAVE
(7-4)/(2-1)=3/1 OR A SLOPE OF 3.
NOW USING ONE SET OF POINTS SOLVE FOR THE Y INTERCEPT (b) IN THE EQUATION 
Y=mX+b (m)= SLOPE
10=3*3+b
10=9+b
b=10-9
b=1 THUS THE LINE EQUATION IS
Y=3X+1.
NOW SETTING X=4 & SOLVING FOR Y WE GET
Y=3*4+1
Y=12+1
Y=13 OR THE ADDITIONAL POINT IS (4,13).
{{{ graph( 300, 200, -6, 5, -10, 10, y = 3x +1) }}} (graph 300x200 pixels, x from -6 to 5, y from -10 to 10, y = 3x +1).