Answer:
y = m x + b equation of straight line
When x = 0 then y = 6 (from graph)
y = m x + 6
When y = 0 then x = 3 and m = -2
y = - 2 x + 6 is the equation of the line
m m' = -1 for perpendicular lines (gradient = 1 / 2)
y = x / 2 + 6 for a perpendicular line (if x = 0 then y = 6)