ANSWER: -1/4
Step-by-step explanation:
4x-y=9
y=4x-9
(so slope/gradient of this line is 4 as y= mx+c and the coefficient of x here is 4)
(formula for perpendicular slopes) m1 multiplied by m2 = -1, where m= gradient
So, m1 x 4= -1
m of perp line= -1/4