Here is a simple little web site that helps you calculate Spell Resistance, or the Difficulty Class (DC) for Saving Throws, or even those pesky Dispel Magic rules.
The rules are for the D&D 3.5 (Dungeons and Dragons 3.5 edition).
https://www.tabletoprpgportal.com/35rules/sr.html
Just plug in your numbers and find out if you succeed in overcoming your opponent's SR, or figure out the DC for your spell, or see if your Dispel Magic succeeds against your enemy.
Very simple to use!
