Danni walked 2 miles, and wendi walked 10,500 feet. which statement is accurate?

For this case what we have to take into account is the following conversion of units:
 1 mile = 5280 feet
 Therefore we have:
 For Danni:
 (2) * (5280) = 10560 feet
 For Wendi:
 10500 feet
 The difference is:
 10560-10500 = 60 feet
 
 Danni walked 60 feet more than Wendi

What do you mean by that?

Aand b are correctly balanced reactions. they have the same number of atoms in both sides of the reaction