Looking for a picture of an HP ProBook 430 which showed a keyboard large enough to read the keys well, J'ai trouvé this image:
It shows an Fn key between the Ctrl key (actually called Strg in this picture, since the picture shows a German version) and the Start ("Windows" logo) key. Hold that down, and then the picture shown indicates M, J, U, 7 correspond to Numpad 0, 1, 4, and 7. So, there is a way to use a Numpad by holding down Fn.
Try holding down Alt and pressing 0128 on the numpad. So, to do that on this computer, hold down Alt, then hold down Fn, and press M. Then, release Fn and hold down Fn again, and press J. Then, release Fn and hold down Fn again, and press K. Then, release Fn, and hold down Fn again, and press 8. Then release Fn. Finally, release Alt. (Yes, vous devriez hold Alt down the entire time.)
If ça fonctionne well, you may wish to try again by just holding Alt, holding Fn, and typing MJK8 (without needing to keep releasing Fn), and then just release Fn and then Alt finalement.