That's not its IV, that's its Characteristic. A Pokemon's characteristic indicates its highest IV:
List of characteristics
"Capable of taking hits" means its defence has the highest IV.
Serebii has an IV calculator here, but for a more simple version of the calculator, go to Psypoke.
If you have already EV trained it, you need to reset its EVs (unless you have kept track of the training) to be able to tell its IVs. Bagon cannot reach over 218 speed, so I assume you're talking about its evolution Salamence.
With a nature that gives neutral speed, Salamence's speed (with full EVs) will be 299.
With a nature that boosts speed, its speed (with full EVs) will be 328.
With a nature that decreases speed, its speed (with full EVs) will be 269.
- these are all assuming it has full IVs in speed.
With Hasty, no IVs, it will get a speed of 294. With Hasty, full IVs, it will get a speed of 328.
You can always increase speed with a Choice Scarf, but Salamence is better off with a Dragon Dance set (which will increase speed), mainly so it's not locked into one move.