The monthly cost is
30+0.05n
if we call the number of texts n.
Heather wants to keep this less than 60, so the inequality is:
30+0.05n<60
Step-by-step explanation:
Note that we can also subtract
30
from each side:
0.05n<30
We can also divide both sides by
0.05:n<600
This is the most useful inequality since it tells Heather she needs to send fewer than 600 texts per month or about 20 per day.