Welcome to the ECF! It sounds like you do not have additional PG to mix with it, so here are two examples that use only your 25mg nic, VG and flavoring to make 10ml of e-liquid. Without additional PG, you will be unable to get a specific PG/VG mix, as it will only be the VG and flavoring that you are using to cut the nic.
For 10ml of juice at 18mg, 82PG/18VG mix and 10% flavoring:
7.2ml 25mg nic
1.8ml VG
1 ml flavoring
And another example for 10ml of juice at 18mg, 75PG/25VG mix and 5% flavoring:
7.2 ml 25mg nic
2.5ml VG
.3ml flavoring