First part:
Since, Dawn pays $32.00 a month, plus $0.75 for each minute over the allowed minutes in her plan.
Let 'm' be the extra minutes used by Dawn over the allowed minutes in her plan.
So, Total bill =

Total bill of Dawn =

So, the expression which shows Dawn's bill for one month is:

Second part:
Dawn received a bill for $47.00 last month.
Since, the expression for Dawn's bill for one month is:
Total bill =





Therefore, Dawn used 20 minutes her phone beyond the allowed minutes.