$$ Part $($c$)$

Given that the thin layer of water has thickness dd$,$ let mm be an integer. What is the proper condition for the the layer to be an anti$-$reflective layer?

$2$d$=($m$+12)$nplexiglas$2$d$=($m$+12)$nplexiglas$/$nwaternwater$2$d$=$m$2$d$=$m$/$nwaternwater$$d$=($m$+12)$nwaterd$=($m$+12)$nwater$/$nplexiglasnplexiglas$2$d$=($m$+12)$nwater$2$d$=($m$+12)$nwater$/$nplexiglasnplexiglas$$d$=$mnplexiglasd$=$mnplexiglas$/$nwaternwater$$d$=($m$+12)$d$=($m$+12)$$/$nwaternwater$$d$=($m$+12)$nplexiglasd$=($m$+12)$nplexiglas$/$nwaternwater$2$d$=$mnwater$2$d$=$mnwater$/$nplexiglasnplexiglas$2$d$=$mnplexiglas$2$d$=$mnplexiglas$/$nwaternwater