How do you set up this?I am lost

Question

Find an equation for the linear model of the situation below and use it to make a prediction. A train is traveling north at a constant rate. At 3:00 P.M. it is 55 miles north of a city. At 4:15 P.M. it is 80 miles north of the city. If d represents the distance in miles, and t represents the time in hours, how many miles north of the city will the train be at 5:45 P.M.?

Answer 1

x = xi + v t
80 = 55 + v(75 minutes)
v = (80-55)/75 = (1/3) mile/min
so
x = 55 + (1/3) t if t in minutes
or
x = 55 + (20) t if t in hours

at 5:45 t = 2:45 = 2.75 hours

x = 55 + 20(2.75) = 110 miles

Answer 2

My answer book had
64t+ 55
d= 231
I don't understand how they came up with these #'s