You can also refer to
Automatic License Plate Recognition library & this query. This will also give you some idea about how to approach things,and how existing solutions are.
But as answered by paul, you should first try to find the rectangular number plate from the complete image and then binarize it and then use the OCR libraries available (Tesseract would be recommended)
You can refer to this link which will help you find the rectangular plate. You need to use openCV libraries, so you will not need alot of math but yes a basic understanding of what is happening behind the scenes can help you solve the problem in better way.
