An Electrician Charges a Flat Fee of $90 for a Home

Multiple Choice

An electrician charges a flat fee of $90 for a home service call. In addition he charges $25 for every 20 minutes as labour cost. If one writes an equation to calculate total charges in terms of hours of labour, what will be the slope of the line?

A) 25
B) 90
C) 50
D) 75
E) 100