Answer:
D
Step-by-step explanation:
Factor the numerators/ denominators
10 - 5 = 5(2a - 1) ← common factor of 5
4a² - 1 = (2a - 1)(2a + 1) ← difference of squares
[ Change ÷ to × and turn second fraction upside down ]
=
× 
[ cancel the factor (2a - 1) on the numerator/denominator ] leaving
=
= 
EXPLANATION
Price of shoes = $5.50
Markup= 40%
Let's call x to the unknown final price.
The markup percentage relationship is given by the following formula:

Replacing terms:

Multiplying both sides by 5.5:

Dividing both sides by 100:

Adding 5.5 to both sides:

Simplifyng the fraction:

Adding numbers:

Switching sides:

Answer: The final price of the shoes in the deparment store is $7.7