Question 1164747
Robert is thinking that his father is 7 years older than twice his age,
f = 2r + 7
his grandfather is 4 years less than twice his father’s age.
g = 2f - 4
If Robert’s grandfather is 70 years old, 
g = 70
:
Replace g with 70 in the 2nd equation
2f - 4 = 70
2f = 70 + 4
2f = 74
f = 74/2
f = 37
:
how old is Robert ?
in the first equation, replace f with 37
2r + 7 = 37
2r = 37 - 7
2r = 30
r = 30/2
r = 15 yrs is Robert's age
:
: