Question

a taxi service charges an initial fee of $5 plus $1.80 per mile. How many miles can you travel for $12

Answer 1

first you need to write an equation or an inequality.

5+1.80x<=12 
the x here is how many miles you are paying for, now you just solve for x. 

5+1.80x<=12
-5                 -5

1.80x<=7
/1.80         /1.80
x<=3.8

you can travel only three whole miles, you do not have enough money to go four full miles.