Several platforms host updated, step-by-step solutions for both volumes:
Tom Apostol's Calculus (Volumes 1 and 2) is widely regarded as one of the most rigorous and comprehensive introductions to the subject, famously blending calculus with linear algebra. For many students, the difficulty of the exercises makes a reliable (solution manual) an essential study companion.
A highly recommended modern resource is the Solutions Calculus Vol 1 2th Edition by Luis Francisco Gomez Lopez. This is an ongoing project that provides clean, digital solutions for the 1988 second edition.
