Most university libraries keep a copy of the solution manual at the reserve desk. You can use it for 2 hours at a time—free.

Pearson (the publisher) releases a companion manual for each edition. For example:

The story of the solutions to Thomas' Calculus is a multi-generational saga of refinement, transforming from a 1951 classroom experiment at MIT into a global pillar of STEM education. The MIT Genesis

For over seven decades, Thomas' Calculus (formally titled Thomas' Calculus: Early Transcendentals or simply Thomas' Calculus ) has been the gold standard textbook for college-level calculus. Authored originally by George B. Thomas Jr. and now in its 14th and 15th editions, this text is renowned for its rigorous approach, clear explanations, and challenging problem sets.