There are two different kinds of normal tables that are used, 
and some people don't use tables at all, but either the TI-84 
calculator or the computer program Excel. 

Using tables:

If you have the kind of table that has both negative and positive z 
values in it, then you'll find the values .7995 and .8023, because 80%
or .8000 is between those two numbers. That is, the z-value entry which 
is closest to having 80% of the area to the left of it. It's a matter of
looking through the body of the table until you find the entries which
.8 is between:   Those listings correspond to z-values 0.84 and 0.85.  
Since .7995 is closer to .8000 than .8023, we choose z-value 0.84.

If you have the kind of table that has only positive z-values, then you
subtract .8 - .5, getting .3. then you'll find the values .2995 and .3023,
because .3 (or .3000) is between those two numbers. That is, the z-value 
entry which is closest to having 30% of the area to the right of the
middle. the left of it. It's a matter of looking through the body of the 
table until you find the listings correspond to z-values 0.84 and 0.85.  
Since .2995 is closer to .3000 than .3023, we choose z-value 0.84.

From either table, we get z = 0.84

Then we use the formula

x = m + sz 

x = 64.5 + (2.4)(0.84) = 66.516

If you use a TI-83 or 84 calculator,

Press 
2nd 
VARS
3

Then type
.8
,  the comma key
64.5
,  the comma key again
2.4
)  the close parenthesis key

(The screen should now read invNorm(.8,64.5,2.4)

press

ENTER

Read 66.51989096

Edwin