I graduated with a gpa of 3.31 and a bachelors in physics. I took a year hiatus and abused my brain with weed, alcohol, and other numb minding distractions. I am now really retarded and can't solve basic math equations.

What can I do to get back to where I was? What books should I read? I wasn't the best and solving math and physics problems but I could definitely pull my weight. My IQ has dropped 50 points. I just want to solve basic arithmetic again at this point.