$3\mathrm{.}5\mathrm{.}9$ WP What is the minimum height for an oil $\backslash (($S G$=0\mathrm{.}75)\backslash )$ manometer to measure airplane speeds up to $\backslash (30\backslash$mathrm$\{$~m$\}/\backslash$mathrm$\{$s$\}\backslash )$ at altitudes up to $1500$ m $?$ The manometer is connected to a Pitot$-$static tube, as shown in Fig. P$3\mathrm{.}5\mathrm{.}9.$

FIGURE P$3\mathrm{.}5\mathrm{.}9$