One possible system is
1x + 3y = 4
2x + 6y = 8
Note how 2 is twice as large as 1, 6 is twice as large as 3, and 8 is twice as large as 4.
In other words, the second equation is the result of multiplying both sides of the first equation by 2.
1x+3y = 4
2*(1x+3y) = 2*4
2x+6y = 8
Effectively the two equations in bold are the same which produces the same line. The two lines overlap perfectly to intersect infinitely many times. An intersection is a solution.
