In one u. s. city, the taxi cost is $2 plus $0.90 per mile. if you are traveling from the airport, there is an additional charge of $3.00 for tolls. how far can you travel from the airport by taxi for $18.50

Working backwards:

The total paid is $18.50.  This includes an up-front charge of $2.  There's a charge of $0.90 for every mile traveled.  And there's another charge of $3 for tolls.  Add together the $2 and $3 (obtaining $5) and subtract this sum from the total:  

$18.50
-   5.00

$13.00

So the mileage charge is $13, and must be ($0.90/mile)(x miles)

Divide both sides of this equation by $0.90 to obtain x, the max distance you can travel in this cab for $18.50.

Idrk but i think u should figure out the n dia n then the units it will make it way more easier