Given Line x+3y=7
x+3y=7; written in the slope intercept form will be
y= -(1/3)x + (7/3) where the slope will be -1/3 then the slope of the perpendicular line to this line will be 3.
as m1m2=-1
writing the new equation in the point slope form we have
(y-1) = 3(x-0)
the equation will be:
y = 3x + 1