That depends on whether you are using a 1-tail test or a 2-tail test.

If it's a 1-tail test, it's the z-value that has the entire area of 0.10 to
the right of it, and therefore it has an area of 0.95 before it.

On your T-84

Press 2ND VARS 3

Make the screen read

area:0.95
μ:0
σ:1
Paste

Use down arrow key to scroll to highlight Paste

Press ENTER

Read

invNorm(0.95,0,1)

Press ENTER

Read 1.644853626 round as your teach said, probably to 1.645

--------------------------

If it's a 2 tail test, it's the z value that has area of one-half of 0.10 to
the right of it, and therefore it has an area of 0.90 before it. 

On your T-84

Press 2ND VARS 3

Make the screen read

area:0.90
μ:0
σ:1
Paste

Use down arrow key to scroll to highlight Paste

Press ENTER

Read

invNorm(0.90,0,1)

Press ENTER

Read 1.281551567 round as your teacher said, probably to 1.28

Edwin