In a colored-counter model, an integer is represented by a set of counters--red and black discs are often used. Black counters represent positive unit values and red counters represent negative unit values. If all the counters are used each time, list all the integers that can be represented with (a) 8 counters (b) 15 counters (a) The following integers can be represented by 8 counters. (Use a comma to separate answers as needed. Use ascending order.)