For this problem, you first plug y=3x-14 in to x+3y=4
The equation will thin look like this:
x+3(3x-14)-14
since the value of y is equal to 3x-14, that means that 3y=3(3x-14)
then you distribute 3 into 3x-14
it will look like this:
3*(3x)+3*(-14)
(9x)+(-42)
9x-42
now you should have written x+9x-42=14
next, combine like terms
x+9x-42=14
10x-42=14
+42 +42
10x=56
now, you divide 56 by 10
10x=56
10 10
x=5.6
okay, now that x has been solved for, we now need to find the value of y
the simplest way to go about this is to choose the equation that already has y by its-self.
y=3x-14
plug 5.6 in to x
y=3(5.6)-14
now solve for y
y=(16.8)-14
y=2.8
FINAL ANSWER
y=2.8
x=5.6
if you want to check your work, you can plug x and y into either equation
x+3y=14
(5.6)+3(2.8)=14
5.6+8.4=14
14=14
y=3x-14
(2.8)=3(5.6)-14
2.8=16.8-14
2.8=2.8
I hope this helps.