Given a distribution of scores with a mean of 26 and standard deviation of 6. assuming normality
what percentage of the cases fall between 18 and 27,
what percentage of the cases lie above score 18 and
below 29
Z = (score - mean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportions cut off by the appropriate Z scores.
I leave you to do the calculations.