I need a second equation so the system has no solutions. {y=3/4x-4

Line b is a direct variation.

Step-by-step explanation:

Here we have 4 lines a,b,c,d . We are required to answer direct variation i.e. lines for which values of y are changing for a single value of x ! Let perform vertical line test to check this.

Vertical line test  means sketching various vertical lines in graph and if every vertical line cuts graph in only one point so it passes this test i.e. for every unique value of x there's only one value of y.

For line a:

Line a is line passing through point (0,1) which passes vertical line test.

For line b:

Line b is a vertical line which have many values of y for x=-4 which fails vertical line test and so it is a direct variation.

For line c & d:

Both of Lines c & d are parallel to each other and passes vertical line test.