The correct option is D there are 4 values of y in [0,4π] for x∈R
x+y=2π3⇒y=2π3−x
∴sinx=2sin(2π3−x)
⇒sinx=2[(√32)cosx+12sinx]⇒sinx=√3cosx+sinx⇒cosx=0⇒x=(2n+1)π2, n∈Z
⇒y=2π3−nπ−π2
⇒y=π6−nπ, n∈Z
Hence, for x∈[0,4π],
x=π2,3π2,5π2,7π2
and for y∈[0,4π],
y=π6,7π6,13π6,19π6