Let teacher =T and Student =S Total age of a teacher and three student =4×20 =80‌ years ‌
⇒‌‌T+35=80‌‌‌‌‌⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅(i) ‌ and ‌‌‌T−S=20 ⇒‌‌S=T−20‌‌‌‌‌⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅(ii) ‌ From ( ‌i‌ ) and (ii), we get, ‌ T+3(T−20)‌‌=80 ⇒T+3T−60‌‌=80 ⇒4T‌‌=80+60 ⇒4T‌‌=140 ⇒T‌‌=35 Hence, the age of the teacher =35 years