x= age of mom
y= age of son
x = 21 + y
(mom is 21 years older than the son)
(x + 6) = 5 (y + 6)
(in 6 years, mom will be five times older than the son)
substitute the known value of x (that's 21+y)
21 + y + 6 = 5(y + 6)
add like terms and multiply to get
27 + y = 5y + 30
subtract 30 from each side
-3 + y = 5y
subtract y from each side
-3 = 4y
divide by 4
-3/4 = y
since we're talking about years
-3/4 x 12 months= -9 months
the father is "inside" the mother
