If I'm guessing the meaning correctly, we're supposed to be familiar with the underlying "philosophy" of AX paper, as outlined

**here**; namely, that AX sheets (A3, A4, A5, etc) have dimensions that are always (approximately) in the ratio of width:length = 1/sqrt[2], and that "adjacent" paper sizes have dimensions in the same ratio.

I

*think* this exercise is asking you to scale the current dimensions of an A4 sheet, pretend that these new values are the actual dimensions of an A4 sheet, and then use the ratio between "next" sizes to find the new values of the dimensions of what would be a new sheet of A3.