Larry used a pattern of colors to make a cube train he use Red Cube a blue cube a Red Cube and another Red Cube before he started the pattern again he use 15 cubes how many red cubes did Larry use

To answer this you can create the pattern up to and including the 15th term.

Red, Blue, Red, Red

Red, Blue, Red, Red

Red, Blue, Red, Red

Red, Blue, Red

Gary used 11 red cubes to make his cube train that was 15 cubes long.