Question 158951
I think you meant to write 
{{{100+4x=129}}}
He's saving money to buy the PS2 for $129.
He starts out with $100. 
The first week he saves, x, so his total is 100+x.
The second week he saves another x, so his total is (100+x)+x or 100+2x.
I think you see the pattern here.
Third week, (100+2x)+x or 100+3x.
After 4 weeks he will have 100+4x.
His goal is $129.
Set those two equal to each to find out what x should be.
{{{100+4x=129}}}
{{{4x=29}}}
{{{x=29/4}}}
x=$7.25
He needs to save $7.25 per week to buy the PS2.