Question

5x-2=y, 10x=4+2y

Answer 1

Put each into the standard form:

5x-y=2
10x-2y=4

You will notice that the second equation is exactly twice (two times) the first.
This is a case where the two straight lines coincide and parallel.
Thus there is an infinite number solutions.

Simply assume any real value for x, and solve for y, and it will be a solution of the system.