The table below shows the cost of different numbers of goldfish at a pet store. ​
COST OF GOLDFISH
​
​Number of Goldfish Cost​
5​ ​ $1.50
​ 10 ​ $3.00
​ 15 ​ $4.50
​ 20 ​ $6.00
​​The cost is a linear function of the number of goldfish. Which statement describes the rate of change of this function?​​

A. The cost increases $0.30\$ 0.30$0.30 each time 111 goldfish is added.

B. The cost increases $1.50\$ 1.50$1.50 each time 111 goldfish is added.

C. The cost increases $3.00\$ 3.00$3.00 each time 555 goldfish are added.

D. The cost increases $6.00\$ 6.00$6.00 each time 555 goldfish are added.