The requirements for standard form of a linear equation in 2 variables (x and y, for instance) is that it be written in the form ax + by = c where:
1. a, b, and c are all integers;
2. a ≥ 0;
3. a, b, and c can have no common factor other than 1.
4. a, b, and c cannot all be 0. (Otherwise you have the trivial equation 0=0.)
5. a and b cannot both be zero if c is not equal to 0 also (Otherwise you have 0 equal to a non-zero number, which is not true.)
If either a, b, or c is irrational, requirement (1) above can be relaxed.
However all of these given equations meet those requirements, except for (2). The -8 should be subtracted from both sides resulting in:
-7y = 28
Or, if this was supposed to be -8x, then multiply both sides by -1, resulting in:
8x + 7y = -20
Rule (2) requires the coefficient of x to be non-negative.
These equations cannot be solved. There must be 2 equations in 2 unknowns to solve them.
You can convert them to slope-intercept form so that you have y = some expression involving x and a constant. You could also convert to x-intercept form so that you have x = some expression involving y and a constant.
