This study focuses on people who have either advanced colorectal cancer or advanced pancreatic cancer that is driven by a gene known as RAS. The purpose of the study is to evaluate the safety of an investigational drug called RMC-9805 in combination with chemotherapy medicines, with or without another experimental drug called RMC-6236. The study will test RMC-9805 and RMC-6236 at different doses with a fixed, standard dose of combination anti-cancer therapy. Study procedures include physical exams, questionnaires, collection of blood and urine samples, echocardiogram, electrocardiograms, computed tomography scans, biopsies, and administration of study drugs.