First get the same denominator 2/5=4/10 so from here do 7/10-4/10 the denominator stays the same and the numerator changes, 3/10 is the answer so Heather live 3/10 of a mile closer to the library than the school
it really depends on how much there is in your order, but if its more than 10 i would use $20 off 10 because its less stuff so the prices would go lower.. if that makes any sense