This is a pretty challenging problem that involves the peroxisomal fatty acid oxidation process. It would be a good idea to review the lecture notes on peroxisomal oxidation. Erucic acid (22:1∆13) is the fatty acid that is found in rapeseed oil that was determined to be undesirable and through selective breeding, has been almost eliminated in modern canola oil. Due to its length, it tends to be first oxidized in the peroxisome to convert it to oleic acid (18:1∆9).