Please tell me what’s the question. So I can answer.
-1x=13+9y
(13+9y)+7y=-19
13+16y=-19
16y=-6
•Y=6/16
-1x-(9•6/16)=13
-1x-3.375=13
-1x=16.375
•X=-16.375
We are given equations as

Firstly, we will write in slope intercept form of line
y=mx+b

Subtract both sides by 4x


now, we can divide both sides by a

we can find slope
so, we get

we are given second equation as

Firstly, we will write in slope intercept form of line
y=mx+b
divide both sides by a

we can find slope

we are given both lines are perpendicular
so, the multiplication of their slopes must be -1

we can plug values

now, we can solve for a

Multiply both sides by a


now, we can solve for a
we get
...............Answer
To find this percentage, it will make it easier if it is worded differently. Put it "15 is what percent of 50?"
To find the percentage, simply divide 15 by 50 then multiply that quotient by 100.
15 / 50 = 0.3
0.3 x 100 = 30 = 30%