Does anyone know what a proportional relationship is in math?

Which value is not a solution of 8x^3 – 1 = 0

Select the two pairs of figures that are similar.

Apassenger train and a freight train leave san jose at 3pm, traveling in the same direction. the passenger train is going three times as fast as the freight train. at 6pm they are 240 miles apart. how fast is each travelling? explain your answer and show your