Simply add any of the following options.
Freebase:
1 x 10ml concentrate, and 3 x 10ml 18mg nicotine shot, to make 120ml of 4.5mg e-liquid. (this will be 8.3% flavour)
2 x 10ml of concentrate, and 2 x 10ml 18mg nicotine shots, to make 120ml of 3mg e-liquid. (this will be 16.6% flavour)
Salt:
1 x 10ml concentrate, and 3 x 10ml 20mg Salt Nicotine shots, to make 120ml of 5mg e-liquid (this will be 8.3% flavour)
2 x 10ml concentrate, and 2 x 10ml 20mg Salt Nicotine shots, to make 120ml of 3.3mg e-liquid (this will be 16.6% flavour)
Take all of the hard work out of mixing, and make shortfills at home in seconds!