I'm baffled by this linear map question I found in a textbook.

Find all x's that would make the 2x2 matrix below (denoting a map from R^2 to R^2) equal to both a shear and dilation.

1st row: 1, x

2nd row: 3, 4

I'm not really sure of what procedure I would have to use in order to tackle this type of problem. There don't seem to be many sites out there that cover this topic in depth. If anyone could give any suggestions, it would be great!