It's not too hard if you're reasonably competent at maths. If you have a solid foundation in calculus, are willing and able to grasp new concepts easily and you are good at algebra, then one should be able to keep up fairly easily. Although if you don't do the homework, or any kind of work to keep up for that matter, then it will pile up on top of you much faster than any of the other subjects.
And I ceebs typing out a full solution to a 4U problem. I'd be here till next morning. Just understand that 4U sometimes requires you to have a lot more intuition than is required for 3U. Sometimes you just have to "see" it. I find that this is typically the case with Harder 3U inequalities.