Question 835574
Let john's age be "x" and Martha's age be "y" 
Based on the question, you have the system of equation
x = 4y 
(x-5) + (y-5) = 50 (because it's five years ago) 
Then change them to standard form and you have
x-4y = 0
x + y = 60 
Now let's solve :)*[invoke linear_substitution "x", "y", 1, -4, 0, 1, 1, 60 ]
There you go, John is 48 and Martha is 12
TA-DAH
:D