Question

What is the value of y in the solution to the system of equations?x y = 12x – 3y = –30

Answer 1

x + y = 12 . . . . . . . . (1)
x - 3y = -30 . . . . . . . (2)
(1) - (2): 4y = 42
y = 10.5

Answer 2

`y=10.5`

Explanation:

we have

`x+y=12` ------> equation A

`x-3y=-30` ------> equation B

Multiply by
`-1` equation A

`-1*(x+y)=-1*12` ------->
`-x-y=-12` ------> equation C

Adds equation B and equation C

`x-3y=-30\\-x-y=-12\\ -----------\\-3y-y=-30-12\\-4y=-42\\y=42/4\\ y=10.5`