You break it down into steps. FIrst do the X's. 5x-3x=2x Then you add 18 to both sides and your equation looks like this 2x=22 Divide by 2 on both sides and x=11
The empirical rule says that approximately 68% of any normal distributed data set lies within one standard deviation of the mean.
The same rule states that about 95% lies within two standard deviations of the mean. Using this rule, and the fact that any normal distribution is symmetric about its mean, you have