We will break the polynomial into two groups: $6t^6+9t^4$ and $2t^2+3\text{.}$ $$\begin{aligned} 6t^6+9t^4+2t^2+3\amp=\left(6t^6+9t^4\right)+\left(2t^2+3\right) \end{aligned}$$ the first group has its own greatest common factor to factor out, and with the second group we can write a $1\text{:}$ $$\begin{aligned} \amp=3t^4\highlight{\left(2t^2+3\right)}+1\highlight{\left(2t^2+3\right)} \end{aligned}$$ and now the binomial $\left(2t^2+3\right)$ appears twice and can be factored out: $$\begin{aligned} \amp=\highlight{\left(2t^2+3\right)}\left(3t^4+1\right) \end{aligned}$$