Need to write a equation in point-slope form.

Question

Michael was driving at a constant speed of 60 mph when he crossed the Sandy River. After 1 hour he passes a highway marker for mile 84. Write a equation in point-slope form, and find out what highway marker he will pass 90 minutes after crossing the Sandy River. 

Answer 1

distance = speed*time.  Since Michael drove for one hour at 60 mph, the distance he drove was:

 

distance = (60 mph)*(1 hour) = 60 miles

 

Since Michael drove 60 miles in the one hour and passed milepost = 84 miles, then the Sandy River, where he started, was at milepost 84 - 60 = 24 miles.  The mileposts he passes with time, then, can be modeled as:

 

Milepost = (60 mph)*(time in hours) + (24 miles)

 

This makes sense because when he started out at time = 0, he was at:

 

Milepost = (60)*(0) + 24 = 24 miles

 

After one hour, he was at:

 

Milepost = (60)*(1) + 24 = 60 + 24 = 84 miles

 

So after time = 90 minutes = 1.5 hours, he'll be at:

 

Milepost = (60)*(1.5) + 24 = _____ miles

 

Can you finish it from here?