Answer: The distance left after 20 days is 1350 miles
Explanation:
To calculate the distance, we use the formula:

where,
s = speed of the bicycle = 90 miles/day
t = time taken = 20 days
d = distance travelled = ? miles
Putting values in above equation, we get:

Total distance to the destination = 3150 miles
Distance travalled in 20 days = 1800 miles
Distance left after 20 days = [3150 - 1800] = 1350 miles
Hence, the distance left after 20 days is 1350 miles