Here is what you need:
an adhesive patching kit ($5)
thread matching the color of your pants (~$2)
a sewing machine
Step 1: Size the patch
Next, iron on the patch to adhere it to the pants. Make sure to piece a piece of paper on the inside of the pants so the patch does not adhere to the fabric exposed by the hold. Make sure the iron is dry, heated up, and then use it. This is a quick and easy step!