I am about to start university, I am going to study engineering, and I totally lack the mathematical level that is required as a minimum, that is to say, I have never studied mathematics in my life and I don't even know how I finished my secondary education. How can I study mathematics from 0? I don't even know how to multiply, and it often happens that I think I'm wrong even in basic sums. Many times I gave the wrong money when I was shopping and they took advantage of me without giving me the change.