Question 524176
Plan A 900 + 0.1*x

Plan B 1200 + 0.15(x-8000)

Plan B < Plan A

1200+0.15(x-8000)<900+0.1x
1200+0.15x-1200<900+0.1x

0.15x-0.1x<900
0.05x<900
x<18000