So a line that is perpendicular is a line that intercepts other line at a 90 degree angle.
Slope of perpendicular lines is the opposite sign and the reciprocal of the other.
So if your slope was 2 the perpendicular line would have a slope of -1/2.
So the equation, 2x + y = 3
Can be rewritten as
y= -2x+3
Perpendicular slope: 1/2
Since it intercepts/ passes the coordinates (5,4) it means that those values are included in the function input x and output y.
y=mx+b
4=1/2(5)+b
Solve for b (y intercept)
4-2.5=b
1.5=b
So the equation of the perpendicular is
y=1/2x+3/2 or y=.5x+1.5