We are given
|x - 3x5| = 6 + y
|9 - y + 6| = 21
We are given a condition that y < 0, and this implies that y can range from -1 to -20
For the first equation
|x - 15 | = 6 + y
This is an absolute function, and it can be written in two forms
(x - 15) = 6 + y or -(x - 15) = 6 + y
(x - 15) = 6 + y
x - 15 = 6 + y
x = 6 + y + 15
x = y + 21
-(x - 15) = 6 + y
Open the parenthesis by multiplying through by -
-x + 15 = 6 + y
-x = 6+ y - 15
-x = (-9 + y)
x = 9 - y
The second absolute function is given as
(9 - y + 6) = 21
-y + 15 = 21
-y = 21 - 15
-y = 6
y = -6
Substitute the value of y into the above equations
For the first value of x
x = y + 21
x = -6 + 21
x = 15
For the second equation
x = 9 - y
x = 9 - (-6)
x = 9 + 6
x = 15
When y = -6, x = 15
The answer is 15