Expressions A time line is a useful way to represent important dates and events throughout history. It's common to divide a historical time line into events that occurred either BC (to the left of zero) or AD (to the right of zero). The year you're living in right now takes place in AD. BC AD 0 When performing mathematical operations involving dates, we can think of a historical time line as a number line. On the number line, the years Increase from left to right of zero represents the origin, the years to the right of zero are considered positive numbers and the years to the left of zero are considered negative numbers. Using this analogy, here are some events that might appear on a historical number line: Event Historical Time Line Number Line -776 The first ancient games take place in Olympia, Greece 776 BC Construction begins on the Great Wall of China, 221 BC World War I begins in central Europe. AD 1914 -221 1,914 (or 1914) Use these ideas about time lines and number lines to answer the questions that follow. Part A The year in which the US CIVII War ended was 25 percent later than the year Christopher Columbus set sall from Spain. If c represents the year Columbus set sail, we can write the year the Civil War ended as C+0.25c. Rewrite this expression as a single term.