Suppose my mana regeneration rate was calculated in this way:
ManaRegenRate = 0.01 × (BaseManaRegen + ManaRegenMultiplier × Willpower) × TotalMana
Where willpower is my attribute ranging from 0 to 100 and BaseManaRegen and ManaRegenMultiplier are some constants.
With this formula I would get mana regenerated per second.
How could I rearrange this formula to get the total amount of seconds to regenerate mana from 0 to full?