Consider the following.

(-8, 7); x + y = 13 → y= -x + 13

parallel lines have the same slope. slope is -1

y = -x + b

7 = -(-8) + b

7 = 8 + b

b = -1

(a) y = -x - 1

perpendicular lines have opposite slopes. slope is 1/2.

y = -1/2x + b

7 = -1/2(-8) + b

7 = 4 + b

b = 3

(b) y = -1/2x + 3

5=812a+9+3

step 1: simplify both sides of the equation.

5=812a+9+3

5=(812a)+(9+3)(combine like terms)

5=812a+12

5=812a+12

step 2: flip the equation.

812a+12=5

step 3: subtract 12 from both sides.

812a+12−12=5−12

812a=−7

step 4: divide both sides by 812.

812a /812 = -7/812

a= -1/116

so the answer is

a=   -1/116

the awnser is visionary