You are given
1 mile = (1/3)*(distance to school)
Multiply this equation by 3 and you have
3 mile = (distance to school)
You also know that
(distance ridden so far) +(remaining distance) = (distance to school)
Subsituting given information, this is
1 mile + (remaining distance) = 3 mile
Subtracting 1 mile from this equation gives
(remaining distance) = 2 miles
Alexander has 2 miles more to ride.
