SOMEONE HELPPP PLEASE!! Complete the table to represent the number of seashells in the collection after the first four summers

Answer:
6 number of seashells for 1 Summer. 21 number of seashells for two summers. 36 number of seashells for three summers. 51 number of seashells for 4 summers.
Step-by-step explanation:
15 substituted in for f and x is the the number of summers.