Answer
$\therefore$ $$\text{Q}_2 = 6Q$$
Work Step by Step
$$\text{Volume Flow rate} = \text{Q}$$
$$\text{Volume Flow rate}= \frac{\Delta V}{\Delta t} = A\times v$$
Initially,
$$\text{Q} = A\times v$$
Now, if the water speed doubles and the cross-sectional area of the
pipe triples,
New Volume Flow Rate will be
$$\text{Q}_2 = 3A\times 2v$$
$$\text{Q}_2 = 6\times A\times v$$
$$\text{Q}_2 = 6Q$$
