Answer:
After 4 miles driven by cab the amount would be same in both cities.
Explanation:
Let the number of miles be 'x'.
Given:
In NYC
Flat fee of cab = $4
Per mile charge = $1.25
Total cab charges is equal to sum of Flat fee of cab and per mile charge multiplied by number of miles.
Framing in equation form we get;
Total cab charges in NYC =

In Chicago
Flat fee of cab = $6
Per mile charge = $0.75
Total cab charges is equal to sum of Flat fee of cab and per mile charge multiplied by number of miles.
Framing in equation form we get;
Total cab charges in Chicago =

Now we need to find number of miles driven so that the amount could same in both cities.
Total cab charges in NYC = Total cab charges in Chicago

Combining like terms we get;

using Division Property we will divide both side by 0.5 we get;

Hence After 4 miles driven by cab the amount would be same in both cities.