In YDSE if the source consists of two wave lengths $\lambda_1=4000 \;a^{\circ}$ and $\lambda _2 =4002\;A^{\circ}$ . Find the distance from centre where fringes disappear if $d= 1\;cm; D=1\;m$

Question

$(a)\;20\;mm \\ (b)\;40\;mm \\ (c)\;60\;mm \\ (d)\;80\;mm$