Current Attempt in Progress

In the figure, a string, tied to a sinusoidal oscillator at $\backslash ($ P $\backslash )$ and running over a support at $\backslash ($ Q $\backslash ).$ is stretched by a block of mass m$.$ Separation $\backslash ($ L $\backslash )-1\mathrm{.}2$ m linear density $\backslash (\backslash$mathrm$\{$p$\}=1\mathrm{.}2\backslash$mathrm$\{$~g$\}/\backslash$mathrm$\{$m$\}\backslash ),$ and the oscillator frequency $\backslash (\backslash$mathrm$\{$f$\}=110\backslash$mathrm$\{$~Hz$\}\backslash ).$ The amplitude of the motion at $\backslash ($ P $\backslash )$ is small enough for that point to be considered a node. A node also exists at $\backslash ($ Q $\backslash ).$

$($a$)$ What mass mallows the ovcillator to set up the fourth harmonic on the string?

$($b$)$ What standing wave mode, if any. can be set vp if $\backslash ($ m$=4\backslash$mathrm$\{$~kg$\}\backslash )/$ Give $0$ if the mass cannot set up a standing wavel?