Question 314863
Find the z scores for both values.
{{{z=(x-mu)/sigma}}}
.
.
.
{{{z1=(81-100)/15=-1.267}}}
{{{z2=(119-100)/15=1.267}}}
Find the normal probability value for both of these z scores.
I used EXCEL's NORMDIST function(CUMULATIVE=TRUE).  
{{{P1=0.1026237}}}
{{{P2=0.897363}}}
The probability for the values to lie between 81 and 119 is the difference in probability values.
{{{P=0.897363-0.1026237}}}
{{{P=highlight_green(0.795)}}}