Find how long it takes for $500 to double if it is invested at 6% interest compounded monthly

Which of the following equations are equivalent to -2m - 5m - 8 = 3 + (-7) + m? -15m = -4m -7m - 8 = m - 4 -3m - 8 = 4 - m m - 4 = -7m - 8 -8 - 7m = -4 + m -8 - 3m = 4 - m