Answer :
the original line is y = (1/2)x + 3
its slope is m = 1/2
the perpendicular line would have an slope of -1/m which is -2
if we use the perpendicular line slope, it's equation would be:
y = -2x + b,
using Q(9,4): 4 = -2(9) + b = -18 + b
b = 4 + 18 = 22
so the perpendicular line is:
y = - 2x + 22