.
Y = 10X + 2 (1)
2X + Y = 26 (2)
From equation(1), you just have an expression for Y via X.
Substitute this expression into equation (2). You will get then
2X + (10x + 2) = 26.
Simplify and solve for X
12X = 26 - 2
12X = 24
X = 24/12 = 2.
You just found X: X = 2.
To find Y, substitute this value X= 2 into equation (2). You will get
Y = 10*2 +2 = 22.
Now you have everything to find the difference X-Y.
I leave this last step to you.
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To the tutor @richwmuller :
I agree with you: for many visitors it is the way to get a solution and/or explanation that they practically
will get NEVER and from NOWHERE.
I do it usually 10 - 20 times per day, when I find the problem formulation correct (or close to be correct)
and then I think that my participation will be useful.
Have a nice day (!)