1. Each number on the second line of the table is 5 times that on the first line. Costs are: $1000, $2000, $2500
2. c = 5t . . . t > 0
3. Each number on the second line of the table is 15 times the magnitude of that on the first line. Costs are: $3000, $6000, $7500
4. c = -15t . . . t < 0 . . . . . . . . . . could also be written as c = 15·|x|
5. One constant of proportionality is negative because the domain it operates on is negative and the desired result is positive.