These are simultaneous equations and can be solved using the elimination method.
We’ll name equation 3x-y=14 as (1), and 5x+4y=12 as (2)
Firstly, manipulate equations such that one of the variable terms cancels out, for this particular problem, it is easier to manipulate the -y term in (1) to cancel out the +4y term in (2).
To do so, multiply the entire equation (1) on both sides by 4, it should now look like this:
12x - 4y = 56, we’ll name this equation (3)
Add equation (3) and (2)
Upon its addition, notice that the y terms cancel and you’re left with a simple single term equation,
17x = 68
Divide both sides with 17 to get the value of x, which is 4.
Now we can substitute (1) with x=4, which again Leaves us with a single variable term (y), which can be solved for to give y = -2. Note that you can substitute in any of the equations, and the value of y will be the same.
Hope this helps.