Answer:
The inequality in this case is 100 + 400*t > 500 + 350*t and for B to be cheaper Sophia has to rent it for more than 8 months.
Explanation:
In order to write the inequality we first need to write two equations one for each apartment. For apartment A we have a fixed cost of $100 and a variable cost of $400 that varies according to the time living in there, so we have:
rent = 100 + 400*t
For apartment B we have a fixed cost of $500 and a variable cost of $350 that varies according to the time living in there, so we have:
rent = 500 + 350*t
In order for the total paid in B to be less than for the one in A we need to satisfy the following inequality:
100 + 400*t > 500 + 350*t
400*t - 350*t > 500 - 100
50*t > 400
t > 400/50
t > 8 months
The inequality in this case is 100 + 400*t > 500 + 350*t and for B to be cheaper Sophia has to rent it for more than 8 months.