Question 1100049
John is currently 4 times as old as his daughter, Linda. 
<pre>
{{{matrix(1,7,

(matrix(2,1,"John's", age)),
"",
""="",
"",
4,
""*"",
(matrix(2,1,"Linda's", age))
)}}}

J = 4•L
</pre>
Six years from now, John will be 3 times as old as Linda.   
<pre>
(John + 6 = 3×(Linda + 6)

{{{matrix(1,7,

(matrix(4,1,"John's", age,""+"",6)),
"",
""="",
"",
3,
""*"",
(matrix(4,1,"Linda's", age,""+"",6))
)}}}

  J + 6 = 3•(L + 6)

So you have these two equations:

      J = 4•L
  J + 6 = 3•(L + 6)

Substitute 4•L from the first equation 
in place of J in the second equation:

4•L + 6 = 3•(L + 6)

You finish.

Edwin</pre>