Amount of money in savings account after x weeks: 25+5x
Amount of money in checking account after x weeks: 50+10x
We are trying to find when 50+10x=25+2(5x)
Now all we need to do is solve.
50+10x=2(25+5x)
50+10x=50+10x distribute
both sides are are equal, therefore every week the amount in checking is twice the amount in savings.