Answer:
You need to write an equation for each.
For Andre, he has 100 dollars, and every week gets 5 dollars more. You add the 5 dollars, and Since you don't know how many weeks it has been, use a variable.
100 + 5w
For Elena, she has 10 dollars, and gets 20 each week.
10 + 20w
Now that you know that it has been 4 weeks, you can plug in 4 for the variable for weeks.
Andrew:
100 + 5(4) =120
Elena
10 + 20(4) ==90
Andrew has more money in this time.
To find when they have the same amount, equal their expressions to each other. This means that they will have the same amount (because they are equalled) and you can solve to find the variable, which means the weeks that they are equal at.
Bring the like terms to each side by canceling them out. Since you have positive 10, then subtract 10 to each side. You have 5w, so subtract 5w to each side.
90+5w=20w
90=15w
90÷15=6
6=w
The answer will simplify down to 6 weeks.
