a.
For a distance greater than 10 miles, the cab company offers a $1 discount from the cab fare.
If the normal cab fare is:
C(m)=2+0.5m
Subtract $1 to get the holiday fare:
C(m)=2+0.5m-1
C(m)=1+0.5m
b.
On any normal day the fare for 10 miles is
C(10)=2+0.5*10
C(10)=$7
Any distance greater than 10 miles will result in a fare greater than $7.
During the hollydays she gets a $1 discount, which means that any distance greater than 10 miles will be more than $6
Since she paid $7.50 you can conclude that she traveled more that 10 miles by cab.
c.
Using the expression in a. you can determine the number of miles she traveled by replacing the formula with C=$7.50
C(m)=1+0.5m
7.50=1+0.5m
6.50=0.5m
m=13
She traveled 13 miles.