Let

d = 1,800 mi the distance of the travel

v = the speed of the travel

t = the time of the travel

v + 12 = the speed when traveling 12 mph faster

t - 5 = the time of the travel with speed 'v + 12'

Since distance = speed*time we have:

vt = d follows t = d/v

(v + 12)(t - 5) = d

plug t = d/v into the above equation

(v + 12)(d/v - 5) = d

d = 1800

(v + 12)(1800/v - 5) = 1800

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click here to see the equation solved for v

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v = 60 mph

We need to ignore the negative solution since the speed is a negative number.

The speed of the car was 60 mph.