Two synchronized microwave sources, A and B $,$ are emitting waves of wavelength $4\mathrm{.}0$ cm $.$ Source A is located on the $\backslash ($ x $\backslash )-$axis at $\backslash ($ x$=0\backslash ),$ source B can be moved along the $\backslash ($ x $\backslash )-$axis, and a microwave receiver is fixed on the $\backslash ($ x $\backslash )-$axis at $\backslash ($ x$=86\backslash$mathrm$\{$~cm$\}\backslash ).$ For each of the following positions of source B determine whether the waves from the sources will reach the receiver in phase $($constructive interference$),$ out of phase $($destructive interference$),$ or with a phase difference of $\backslash (\backslash$pi $/2\backslash$mathrm$\{$rad$\}\backslash ).$