Sonu's grandmother is 80 years old and sonu is 20 years old. how many years ago was his grandmother 7 times as old as son? (linear equations in one variable)

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