I have problems dealing with word problems and I hope I can get some help in going in the right direction.

A telephone bill lists a minimum of $7.50 for first 80 message units. What is the additional cost if it's plus 0.06 per unit for the next 60 units, plus 0.05 per unit for the next 60 units, and plus 0.04 per unit for any units beyond 200.

Thanks.

What is the total number of units?

Draw a picture.