\(1 \frac{3}{7} * 5 \frac{4}{3} = \frac{10}{7} * \frac{19}{3} = \frac{190}{21} \approx 9,0476..\)
When he simplified the expression:
\(1 \frac{1}{2} *6= \frac{3}{2} * \frac{6}{1} = \frac{18}{2} = 9\)
\(9,047 \approx 9,05 \approx 9\)
I think Joseph's estimate a close estimate.
