equation of a line passing through from 2 points (x1, y1) and (x2,y2) is given as
y = mx + c
as two points are passing through it so it will satisfy the equation. so putting both points in equation
(x1,y1) = (0,3)
y1 = mx1 + c
3 = m×0 + c
c = 3
putting 2nd point (x2,y2) = (7,0)
y2 = mx2 + c
0 = m× 7 + c
c + 7m = 0
putting value of c from above
3 + 7m = 0
7m = -3
m = -3/7
so putting value of m and c in final equation.
y = mx + c
y = (-3/7)x + 3
so option 3 is your answer