36 mg/mL Nic, you want to dilute to 30 mg/mL. 36/30 = 1.2, so you want to increase the total volume by 1.2. So you add 0.2 mL flavor (of any kind) per mL of nic
juice. Or the whole works - 30 mL * 1.2 = 36 mL total volume. You can add 6 mL of flavoring.
To check this - 36 mg/mL * 30 mL = 1080 total mgs of nicotine. 1080 total mgs nicotine in 36 mL total final volume = 30 mg/mL.
The second you can work out the same way. (48 mg/ML)/ (30 mg nic/mL target) = 1.6. So you add 0.6 mL flavour to dilute. The whole works 30 mL * 1.6 = 48 mL final volume, so you can add 18 mL flavour to the whole batch.
To check this, the same thing:
48 mg/mL nic * 30 mL nic base = 1440 mgs nic total. 1440 mgs nic total/48 mL final volume = 30 mgs nic/mL final mix.