Hey @daisy7! I'll try to guide you on answering all of this problems.
1C. For a, first thing to do is prioritize each group attached to the double bond. If two groups are in the same side, that will be considered as Z (cis). In this case, O-CH3 and the propyl group are in the same side so it appears to be Z. Use the same method in answering b. Johnny fully explains how E/Z nomenclature works here: https://www.clutchprep.com/organic-chemistry/cis-vs-trans/?c_id=14841
1D. For this example, this will require you a lot of sketching since we don't have any shortcut formula to know the # of isomers. Keep in mind that it has an IHD of 1 so the isomer may contain 1 double bond.
1E. This reaction is an SN2 reaction since we are dealing with 2o alkyl halide and a strong nucleophile. You can watch johnny's video on SN2 mechanism here, you can see how the transition state is formed there. https://www.clutchprep.com/organic-chemistry/sn2-reaction/?c_id=14841#content-item-2241
Hope that helps!