Answer: Your answer is going to be D. (10, -1)
Step-by-step explanation:
Starting off the equation you want to get rid of either x or y ( I did x first)
Take x+3y=7 and multiply the entire equation by -2 -- -2(x+3y=7)
You get -2x-6y=-14 and then add the two equations together
-2x-6y=-14
2x-4y=24 -- You get -10y = 10
y = -1
You can take the -1 and plug it back into either equation.. ( I did x+3y=7)
x+3(-1)=7 -- x-3=7 -- Add the 3 to get the 10 ( x = 10 )
So you have x = 10 & y = -1
(10,-1)