Answer:
C
Step-by-step explanation:
this is an arithmetic sequence (we add something from element to element).
"an" describes the salary during the nth year.
a1 = $3000
a2 = a1 + 600
a3 = a2 + 600 = a1 + 600 + 600 = a1 + (3-1)×600
an = a1 + (n-1)×600 = 3000 + (n-1)×600
so,
a15 = 3000 + (15-1)×600 = 3000 + 14×600 = $11400
