The Khan Academy is a good resource, but to re-learn Algebra and Geometry, I would suggest one of the online Math learning systems that are currently in use in self-paced college Math labs. One example that we use at our college is ALEKS (https://www.aleks.com/independent/students). Another product is MyMathLab (http://www.pearsonmylabandmastering.com/northamerica/mymathlab/students/index.html).