The polygons are the same shape; one is just bigger than the other.
Find how many times bigger by dividing the side of one shape by the matching side of the other shape:
\(\frac{16}{12} = \frac{4}{3}\)
And we can check the other side just to be sure that it is the same.
\(\frac{32}{24} = \frac{4}{3}\)
So that means that:
\(\frac{x-1}{6} = \frac{4}{3} \\~\\ x-1 = \frac{(6)(4)}{3} \\~\\ x = 8+1 \\~\\x=9\)