$($Bernoulli$/$continuity$)$ Water flows steadily through the pipe shown in the

figure below such that the pressures at sections $(1)$ and $(2)$ are $319$ kPa and

$110$ kPa $,$ respectively. Determine the diameter of the pipe at section $(2),D_2,$ if

the velocity at section $1$ is $21\frac{m}{s}$ and viscous effects are negligible.