On the TI83:

normalcdf(-E99,70,73,7.8/Ö(24))

Press ENTER.  Get .0297673515

That is a negative sign, not a minus sign. It's found on the key 
on the very bottom right. The sign is in parentheses like this (-)
on the key.

To get "normalcdf(" press 2ND VARS 2.

To get the E, press 2ND then the comma key

To get "Ö(", press 2ND x2.

The comma has a key all by itself.

The "/" is just the division key, ÷

Edwin