John's mother is five times as old as John is.
M = 5J
Three years ago,...
Three years ago, the mother was M-3
Three years ago, John was J-3
Three years ago, she was 9 times his age.
M-3 = 9(J-3)
Solve by substituting 5J for M in the second equation,
solving for J, then substituting what you get to find M.
Edwin