Question

5(2 + 4z) = 85

Answer 1

10 + 20z = 85
20z = 75
divide by 20 on both sides...and z =...?

Answer 2

or
(2 + 4z) = 17
4z = 15
dividing by 4 on both sides, and z=......?

Answer 3

first distribute the 5 to (2 + 4z) to get..
10 + 20z =85 [5 times 2 and then 5 times 4z)

second
subtract the 10 from the left side to have the variable, z, alone
20z = 85-10
so 20z = 75

third
divide the 75 by 20 to get z, your unknown
z= 3.75

fourth
you can ensure that you have the correct answer by plugging in the found value into z
5(2+4*3.75) = 85
5 (2 + 15) = 85
5 x 17 = 85