Remark
The entire trip costs 485 dollars. She has a hundred, and you are looking for the number of weeks needed to save for the trip.
Step one
Set up the basic equation.
35w + 100 ≥ 485
Step two
solve
35w + 100 ≥ 485 Subtract 100 from both sides.
35W ≥ 485 - 100
35W ≥ 385 Divide by 35
W ≥ 385 / 35
W ≥ 11 weeks.
Since we don't have choices, we can't eliminate those that are wrong.
If I had to guess I would say it was something that looked like
35W + 100 ≥ 485