The endpoints of on are located at o(1, 2) and n(3, 1). using slope-intercept form, write the equation of line on.

y = -1/2x +2 1/2
General equation;
y = mx + c

Calculating the slope;
Change in y/ (change in x) = gradient m

(2-1)/(1-3) = - 1/2

Replacing m gives;
y= -1/2x + c

Calculating the value of c
take point (1,2) above and replace y with 2 and x with 1
2=-1/2 *1 +c
c = 2 1/2
Equation then is 
y = -1/2x +2 1/2

Iwould say d but i am not 100% positive