Find all occurrences of the string @$3$G in string TS$1$ and place the locations of the first character of each such substring $($@$)$ into Str$3$G$.$ Example: TS$1=\text{'}\%$@$3$Gb$6$kl@$3$G$9$@$33$G$\text{'}$ returns Str$3$G$=[29]$