Question

Which correctly shows the following equation rearranged for the quantity of interest x
z = 1/3 x (m + y)

x = 3z/m+y
x = m+y/3z
x = 1/3 z (m + y)
m = 3z/x - y

Answer 1

Start from z = (1/3) x (m + y), i.e. z = x(m + y)/3.

Multiply both sides by 3: 3z = x(m + y).

Divide by (m + y): x = 3z/(m + y).

None of your listed forms is written exactly like that. If the first choice x = 3z/m+y were meant as x = 3z/(m+y) (with parentheses), that would be correct; as written it reads (3z)/m + y and is incorrect.