Question 72347
Let J = Jeanne's age and M = Michel's age.  From the problem description, you can write:
J = 3M Substitute this into the equation below and solve for M
J + M = 20
3M + M = 20
4M = 20 Divide both sides by 4.
M = 5 This is Michels's age.
J = 3M = 3(5) = 15 This is Jeanne's age.