Two synchronized microwave sources, A and B, are emitting waves of wavelength 4.0 cm. Source A is located on the x-axis at x = 0, source B can be moved along the x-axis, and a microwave receiver is fixed on the x-axis at x = 82 cm. 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 π/2 rad.
a) x = -8 cm
b) x = -6 cm
c) x = -5 cm
d) x = -4 cm
e) x = -3 cm
f) x = -2 cm