First, get one variable all by itself

-5x-y=3 (add y to both sides)

-5x=y+3 (subtract 3 from both sides)

-5x-3=y

Now, let’s look at the second equation

x-4y=9 (now, we said earlier that y=-5x-3)

x-4(-5x-3)=9 (multiply everything out)

x+20x+12=9 (combine all x’s)

21x+12=9 (subtract 12 from both sides)

21x=-3 (divide both sides by 21)

x=-3/21

now that we know the value of x, let’s re-evaluate our first equation.

-5x-y=3 (we know x=-3/21)

-5(-3/21)-y=3

15/21-y=3 (add y to both sides)

15/21=y+3 (subtract 3 from both sides)

-6/21=y

Now, go solve B

-3/21=-1/7, -6/21=-2/7

-5x-y=3

-5(-1/7)-(-2/7) is not equal to 3

5/7+2/7=1, not 3

since jack got the y=-16/7, then i calculate the x = -1/7, lets check

-5x-y=3

-5( -1/7)-(-16/7)=3

5/7+16/7=3

21/7=3

3=3

lets check x-4y=9

( -1/7)-4(-16/7)=9

( -1/7)+64/7=9

63/7=9

x-4y=9

lets pick x-4y=9, then x=9+4y

substitute to the 1st equation

-5x-y=3

-5(9+4y)-y=3, since we know the x is 9+4y

-45-20y-y=3

-20y-y=3+45

-21y=48

y= -16/7

you should know how to find x now since you know the value of y

now you got the idea, try to solve the 2nd one yourself.