G6.4 It is given that $\sqrt{90}=9.49$, to 2 decimal places.
If $d<7 \sqrt{0.9}<d+1$, where $d$ is an integer, what is $d$ ?
$\begin{array}{l} 7 \sqrt{0.9}=0.7 \sqrt{90}=0.7 \times 9.49 \text { (correct to } 2 \text { decimal places) } \\ =6.643 \\ d=6\end{array}$