Question 29485
Solve by substitution:
1) {{{8y = 15-4x}}} and
2) {{{x+2y = 4}}} Express this one in terms of x and substitute into the first equation then solve for y.

2a) {{{x = -2y+4}}} Substitute for x into equation 1)

1a) {{{8y = 15-4(-2y+4)}}} Simplify and combine like-terms.
1a) {{{8y = 15+8y-16}}} Subtract 8y from both sides of the equation.
1a) {{{0 = -1}}} Never true! 
The solution to this system of equations is the "empty set" or "null set"
This means that the two lines represented by these equations do not intersect, i.e., they are parallel lines.

You can easily verify this parallelism by finding the slope of each line.  You will find that the slopes are the same.
This is left as an exercise for the student!