Measure the distance of the selected line from the Mid-Atlantic Ridge.
Calculate the distance of that line from the ridge on real Earth by multiplying the distance times your map scale.
Determine the spreading rate by dividing the distance by the number of years (age of the seafloor at your selected location).
Find the age of the Atlantic by dividing 4,550 km by your spreading rate.
Be sure to keep your units straight. There are 1000 meters in one kilometer and 100 centimeters in one meter.
Verify your results. Did you find an age in the range of about 180 to 220 million years?
Note that we do not really know the exact year that the Atlantic began forming. A value anywhere in the range of 180 to 220 million years ago is valid. Why do you think the calculated age varies depending on where you measure from?From what era in geologic time did the Atlantic begin forming?