6x - 3y = 21, the ordered pair given is (3, -1)
Let x = 3, y = -1
Substiute the value of x and y into the above equation
6(3) - 3(-1) = 21
18 + 3 = 21
21 = 21 ----- YES
The ordered pair is a solution to the given solution
7x - 6y = 38, the ordered pair given is (2, -4)
Let x = 2 and y = -4
Substitute the value of x and y into the above equation
7(2) - 6(-4) = 38
14 + 24 = 38
38 = 38 --------- Yes
4x - 7y = 13 : (5, 12)
x = 5, y = 12
4(5) - 7(12) = 13
20 - 84 = 13
-64 = 13 ----- NO
-64 is not equal to 13