Question 147217
(1) Let x=number of years ago that the man's age was eight times his son's age
Our equation to solve is:

40-x=8(12-x) get rid of parens
40-x=96-8x subtract 40 from and add 8x to both sides
40-40-x+8x=96-40-8x+8x  collect like terms

7x=56  divide each side by 7
x=8

CK
40-8=8(12-8)
32=8*4
32=32

(2) Let y=the number of years hence that the man will be three times the age of his son
Our equation to solve:

40+y=3(12+y)  get rid of parens

40+y=36+3y  subtract 36 and also y from each side

40-36+y-y=36-36+3y-y  collect like terms

4=2y  divide each side by 2
y=2

CK
40+2=3(12+2)
42=3*14
42=42


Hope this helps---ptaylor