Answer :
Answer:
10 years ago
Step-by-step explanation:
Let x be the number of years ago
x years ago,
Sonu's grandmother was 80 - x
Sonu was 20 - x
x years ago,
the grandmother was 7 times as old as Sonu
80 - x = 7(20 - x)
80 - x = 140 - 7x
6x = 60
x = 10