Question

What is, x+3y=1
-3×-3y=15
Can you show me the steps, confused?

Answer 1

first equation is the line
y = -(1/3) x + 1/3

second equation (-x-y=5) is the line
y = - x - 5

so
-x-5 = -(1/3)x + 1/3

2/3 x = -16/3
x = -8
then y = 3
-------------------
check
-8+9 = ? 1 yes
+24 - 9 = ? 15 yes

Answer 2

there are lots of other ways, like add the two equations
+1 x + 3 y = 1
-3 x - 3 y = 15
---------------- add
-2 x = 16
x = -8 then go back and get y

Answer 3

or substitute
x = 1 - 3y
use that in the second one
-3(1-3y) -3y=15
-3 + 9 y -3 y = 15
6 y = 18
y = +3 again

Answer 4

the first way is brute force finding where two lines hit
The second way is called "elimination".
The third way is called "substitution".

They are all ways o find the intersection of those lines.