24% of 170 Where did he get that result

I guess you mean 67% and not 24%. 67% of 170 is ≈114 but that is for the range 0to170. Our case is -90to80 and, so, 67% of that would be 24.

I´m still confuse about that, but yeah, I refered to 67% and not to 24%.

I know the idea about the professor picked up the last number (-90)  and the first number (80)
But I still dont get the 24%, If I resolve -90 + 80 = -10; If I sum them I obtained the 170, so I dont see the 24 hahaha

I think of -90 to 80 as a number line and, as we have 3 parts on that line; the first part would be -90 to -33, the second one being -33 to +24, and the third one to +80. So it's like
-90   -33   +24    80
<------|------|------>

same as
0      57   114   170
<------|------|------>
(More simplified, -90+57 is -33 and -33+57 is 24, 24+57=81[80])
as 67% of 0to170 is 114, that percentage of -90to+80 is 24.