Answer:
Alex will have the sames savings as Sarah at week 20
Explanation:
Make equations for both savings with this format:
Savings = weekly savings * x + starting money
Alex's savings = 6x + 10
Sarah's savings = 3x + 70
(x = the number of weeks)
Then we change the x value up one value until both matches (or use a graphing tool/calculator (whichever works)).
If we set x = 20 (weeks), both savings will be equal at $130.
Hope it helps.