Solve

x^2-4=77

E2020

x = 9  or  x = -9

Step-by-step explanation:

x² - 4 = 77

then

x² - 4 + 4 = 77 + 4

then

x²  = 81

then

x² - 81 = 0

then

x² - 9² = 0

then

(x - 9)(x + 9) = 0

then

x - 9 = 0  or  x + 9 = 0

then

x = 9  or  x = -9

:)

it is a. 4.2 because 7.6-3.4 gets the remaining length of 4.2. i might be wrong but i am pretty sure this is the answer.