Question

(?,6) is on the line 2x – 7y = 0. What is the other half of the coordinate

Answer 1

If we plug the given value of y = 6 into the equation, we get:
$2x-7\times6=0$
which can be rearranged to
2x = 42
giving x = 21.
Therefore the other half of the coordinate is 21.

Answer 2

(?, 6) is on  2x - 7y = 0 

Let ? be replaced with t for (?, 6)   ? = t,  y = 6

2x - 7y = 0

2*t - 7*6 = 0

2t = 42

t = 42/2

t = 21

the other coordinate is t = 21,  so point is (21,6).