Question 150712
B - Bob's age
F- Bob's father's age
1.{{{F=3B}}}
Four years ago, Bob was B-4 years old and his father was F-4.
2.{{{F-4=4(B-4)}}}
Now you have two equations with two unknowns, you can solve it.
Substitute eq. 1 into eq. 2 and solve for B.
2.{{{F-4=4(B-4)}}}
{{{3B-4=4(B-4)}}}
{{{3B-4=4B-16}}}
{{{-B=-12}}}
{{{B=12}}}
Now use equation 1 to solve for F.
1.{{{F=3B}}}
{{{F=3(12)}}}
{{{F=36}}}
Bob is 12 and his father is 36.
Four years ago, Bob was 8 and his father was 32.