Solve the Problem $a _ { n } = 3 ( 7 ) ^ { n - 1 } ; 1029$

Solve the problem.
-A bacteria culture starts with 7 units and triples every day. Write the general term of the sequence that describes the growth of this culture. Find the number of bacteria units there will be at the beginning of the fourth day.

A) $a _ { n } = 3 ( 7 ) ^ { n - 1 } ; 1029$ units
B) $\mathrm { a } _ { \mathrm { n } } = ( 7 ) ^ { \mathrm { n } } ; 2401$ units
C) $a _ { n } = 7 ( 3 ) ^ { n - 1 } ; 189$ units
D) $a _ { n } = 7 ( 3 ) ^ { n } ; 567$ units