You have to deal with this type of question step by step. Firstly, you can figure out all the unknown values (such as sqrt x-3), by substituting x for 19, as you are trying to figure out f(x) when x=19. Therefore:
x+2=21
sqrt(x-3)=sqrt(19-3)=sqrt 16=4
Now the equation is easier to handle:
3/21 - 4
We can write this as 3/21 - 4/1 , which equals -27/7.
For the first one his car used 8/340 or 2/85 gallons for one mile.
After the fix, his car 7/350 or 1/50 gallons for one mile.
Then you subtract 1/50-2/85 to get (17-10)/850 or 7/850.
You multiply this by 4 to get 28/850 which is $0.0329411
Since it is asking for cents you multiply by 100 to get approximately 3 cents.
