What is the sum of -7/18 and - 3/6 A) 4/9 B)-8/9 C) 4/9 D) 8/9

Atrain leaves little? rock, arkansas, and travels north at 90 kilometers per hour. another train leaves at the same time and travels south at 80 kilometers per hour. how long will it take before they are 680 kilometers? apart?