Find a1 for the geometric series with r=3 and s6=364

Heres how to solve it

An infinite geometric series is the sum of an infinite geometric sequence. This series would have no last term. The general form of the infinite geometric series is a1+a1r+a1r2+a1r3 + ... a1+a1r+a1r2+a1r3 + ..., where a1a1 is the first term and rr is the common ratio