let "a number" = x
(x + 7)/3 = 7
Note the equal sign. What you do to one side, you do to the other. Do the opposite of PEMDAS.
First multiply 3 to both sides
(x + 7)/3(3) = 7(3)
x + 7 = 21
Next, subtract 7 from both sides
x + 7 (-7) = 21 (-7)
x = 14
14 is your number
hope this helps