Frank left his house at 7 a.m. and drove to the airport at a speed of 50 mph. Lance left his house at 6 a.m. and drove to the sa
me airport at a speed of 55 mph. Frank's house is 150 miles from the airport and Lance's house is 220 miles from the airport. At what time did Frank arrive at the airport?
The reason why c = 6n + t is the same as c - t = 6n is because c is the sum of the addition problem. 6n and t are the addends. The inverse operation for addition is subtraction. c is the cost that will be reduced by t. The answer is still 6n.