Question 855746
Plan A 
let total bill be x
she has to pay
50+20%x

Plan B

250+10%x

Plan B < plan A

250+10%x< 50+20%x

250-50 <20%x-10%x

200< 10%x

multiply by100
200*100 <10x
20000<10x
20000/10<x

2000<x

The bill should be greater than $2000