Which expression is equivalent to 1 third b minus 7

When y’all answer can y’all explain too !

Look at the figure below: triangle abc is a right triangle with angle abc equal to 90 degrees. the length of ac is 5 units and the length of ab is 4 units. d is a point above c. triangle adc is a right triangle with angle dac equal to 90 degrees and dc parallel to ab. what is the length, in units, of segment cd?

Cody ran nine miles on his first day of training. the next day he ran 1/8 that distance. how far did he run the second day?