Answer:
6 weeks
Explanation:
Multiply 150 by 0.2 (20% in decimal form) to get how much she saves every week.
150×0.2=30
She saves 30 every week, but you want to get to 180.
Divide 180 by 30, and you get 6
180÷30=6
That means it takes her six weeks to save $180.