\(\widehat{B}+\widehat{C}=90^o\\ \Rightarrow2\widehat{C}+\widehat{C}=90^o\\ \Rightarrow3\widehat{C}=90^o\\ \Rightarrow\left\{{}\begin{matrix}\widehat{C}=30^o\\\widehat{B}=60^o\end{matrix}\right.\)
\(\widehat{A}+\widehat{D}=90^o\\ \Rightarrow\widehat{D}=90^o-\widehat{A}=90^o-30^o=60^o\)