They square root of 0.64 is 0.8
The answer to the question
The first is a. you can rewrite it

the second is d. the only common factor between 20 and 40 that can be taken out is the 4 which becomes a 2, but inside the square roots there is still a 5 and 10, which cannot be combined
the third is c.

the fourth is d.
add 3 to both sides

then square both sides

then divide both sides by 2, x=50