Ive taken calculus 1-3 and differential equations and didnt think they were hard at all. I like math quite a bit so I decided to open Apostol's Single Variable Calculus Book and decided to attempt the problems. I was only able to do 30% of them and figured that Apostol's calculus is way too hard for me. I'm a math major and I know that I'll need to have done Apostols or spviak's books on Calculus for real analysis, but not being able to do Apostol's calculus is really frustrating me. Is there another way I can go? like maybe read an intro to proofs book and afterwards try doing apostols?