77°24′+34°40′=?；108°18′-56°21′=?；15°36′18″×2=?；109°23′18″÷3=

77°24′+34°40′ =77°+34°+24‘+40’ =111°+64‘ =11°+1°4’ =112°4‘ 108°18′-56°21′ =107°+1°18‘-56°-21’ =51°+78‘-21’ =51°+57‘ =51°57’ 15°36′18″×2 =15°×2+36‘×2+18“×2 =30°+72’+36” =30°+1°12‘+36“ =31°2’36” 109°23′18″÷3 =108°÷3+1°23’18”÷3 =36°+81‘÷3+138”÷3 =36°+27‘+46“ =36°27‘46“