To raise money, the student council sells candy-grams each year. From the past experience, they expect to sell 400 candy-grams at a price of $4 each. They also have learned from experience that each $.50 increase in the price causes a drop in sales of 20 candy-grams.

Suppose the student council need revenue of at least $1800. Solve an inequality to find all the possible prices that will achieve their fundraising goal.