A scientific calculator costs $8 x 2 = $<<8*2=16>>16.
A graphing calculator costs $16 x 3 = $<<16*3=48>>48.
So, she spent $8 + $16 + $48 = $<<8+16+48=72>>72 for the three calculators.
Therefore, the math teacher received $100 - $72 = $<<100-72=28>>28 change.
#### 28