On tuesday and wednesday , cab fare cost $7.75 total. on monday and thursday , cab fare cost $6.30 on each day. on friday , cab fare cost $ 7.00. what was the average daily cost?

The average daily cost is $7.02.
 
to get the average cost you add up all the prices

 7.75
 7.75
 6.30
 6.30
+7.00
35.10

then you divide that by the amount of numbers you have

35.10 / 5=7.02
 
then there's your answer.