A Gallery of Groups · Easy problem

A dial has $26$ equally spaced marks, numbered $0$ through $25$ clockwise. It is sitting at mark $19$. Pressing a button advances it clockwise by a fixed step size $x$ (added once, mod $26$), and one press lands it on mark $4$. What is $x$, as the representative in $\{0,1,\ldots,25\}$?