They are 'scientific' equivalents to each other, meaning if you had a scientific calculator and entered the "DEC" (decimal) number and converted to "HEX" (hexadecimal), they would be representative of the same amount to each other. Just enter the DEC numbers into your scanner for the talkgroups and you will do fine.
HEX is used for programming Motorola radios, but scanners use DEC mostly to track trunk systems. Some scanners can accept HEX programming if it is something the owner choses to use.
As
n4yek has stated, any scientific calculator can convert DEC (Decimal) to HEX (Hexadecimal) and vice versa. We normally deal with DEC in the scanner world with a few exceptions, again noted by
n4yek.
Windows computer operating systems, by default, include a calculator and all you need to do is open the calculator and click on View > Scientific and using the radio buttons on the left side under the display, you, too, will be able to make those conversions.
The reason behind having the radios use Hexadecimal when they are programmed is Motorola systems use a status bit in the TG.
The RR Wiki has a discussion concerning status bits here. In a Motorola system, all TGs that do not carry a status bit can be divided evenly by 16. This can also tell you which status bit a TG is carrying if it is not evenly divisible by 16. Normally, when scanning, we want the "raw" TG (without status bits) programmed into the scanner.