Answer: 
12
Step-by-step explanation: So the straight line is given by the equation: y = k * x + by=k∗x+b
Let write line L as: y_1(x) = k_1 * x + b_1y 
1
 (x)=k 
1
 ∗x+b 
1
 
Line L: 4 * y - 6 * x = 334∗y−6∗x=33
Let write line L in general form: y = \dfrac{33 + 6 * x}{4} = 1.5 * x + 8.25y= 
4
33+6∗x
 =1.5∗x+8.25
From L line's equation: k_1 = 1.5k 
1
 =1.5 , b_1 = 8.25b 
1
 =8.25
Let write line M as: y_2(x) = k_2 * x + b_2y 
2
 (x)=k 
2
 ∗x+b 
2
 
Perpendicularity condition of two lines is: k_2 = - \dfrac{1}{k_1}k 
2
 =− 
k 
1
 
1
 
k_2 = -\dfrac{1}{1.5} = -\dfrac{2}{3}k 
2
 =− 
1.5
1
 =− 
3
2
 
Substitute the numbers in M line's equation:
M: y_2(x) = -\dfrac{2}{3} * x + b_2M:y 
2
 (x)=− 
3
2
 ∗x+b 
2
 
Let put in this equation values from point A(x_a = 5, y_a = 6)A(x 
a
 =5,y 
a
 =6)
M: 6 = -\dfrac{2}{3} * 5 + b_2M:6=− 
3
2
 ∗5+b 
2
 
b_2=6 + \dfrac{2}{3} * 5=\dfrac{28}{3}b 
2
 =6+ 
3
2
 ∗5= 
3
28
 
Substitute b_2b 
2
  in M line's equation:
M: y_2(x) = -\dfrac{2}{3} * x + \dfrac{28}{3}M:y 
2
 (x)=− 
3
2
 ∗x+ 
3
28
 
Let put in this equation values from point B(x_b = -4, y_b = k)B(x 
b
 =−4,y 
b
 =k)
M: k = -\dfrac{2}{3} * (-4) + \dfrac{28}{3} = \dfrac{8+28}{3}=\dfrac{36}{3}=12M:k=− 
3
2
 ∗(−4)+ 
3
28
 = 
3
8+28
 = 
3
36
 =12
k = 12k=12