2x - y = 7 ------------------- (1)
6x - 3y = 14 ----------------(2)
To solve a pair of simultaneous equations, you can use either of the Substitution method or the Elimination method. If one of the variables (either x or y) has a coefficient of 1, then the substitution method is a prefered one.
Looking at equation (1), when y crosses to the other side of the equation and 7 similarly crosses to the left, then you have
2x - 7 = y
(When a positive value crosses the equality sign, it becomes a negative value, and vice versa)
If y = 2x - 7, then substitute for the value of y (2x - 7) into equation (2)
6x - 3y = 14
6x - 3(2x - 7) = 14
6x - 6x + 21 = 14
0 + 21 = 14
21 = 14
As you can see, 21 does not equal 14, and that only leads to the conclusion that these pair of equations has no solution.
If we decided to use the elimination method as a check for accuracy, we would have;
2x - y = 7 -------------------(1)
6x - 3y = 14 ---------------(2)
We start by multiplying equation (1) with 6 and multiply equation (2) with 2. Note that 6 and 2 are the coefficients of x in both equations (1) and (2).
2x - y = 7 ------ x6
6x - 3y = 14 ----x2
12x - 6y = 42 --------------- (3)
12x - 6y = 28 --------------(4)
Subtract equation (4) from equation (3)
0 + 0 = 14
0 = 14
This also is not possible as you can see, and still goes on to show that the equations has no solution.