A linear equation does not actually have solutions; rather, we find the locus of points ( x, y = f(x) ) and draw a straight line through them.
It is a SYSTEM of linear equations that may or may not have solution(s).
If one equation in this system is a multiple of the other, then the two equations represent the same line and the SYSTEM has infinitely many solutions. The graphs of the two equations coincide/overlap.
An equation can have infinitely many solutions when it should satisfy some conditions. The system of an equation has infinitely many solutions when the lines are coincident, and they have the same y-intercept. If the two lines have the same y-intercept and the slope, they are actually in the same exact line.
You can answer this problem using the midpoint formula, but we can work out the 4th vertex by just logically thinking it through by first drawing out the rhombus on an x-y coordinate plane. I wrote the answer out on paper since it is easier than typing. Let me know if you have any questions.
