Hi Joseph,
Sophia is a good source for the College Algebra requirement for your degree plan. They do have an open tutorial throughout the course that can be used during the challenges as well as the Milestones.
Also, another suggestion is the one we discussed with the TESU Liberal Arts Math TECEP. I gave you some links and information on that earlier this week.. Please send me an email once you have checked those sources out for the prep courses and let me know what you think.
Happy Studying!
Angela